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AGRICULTURAL METEOROLOGY 



tlbe IRutal TLcxUJBooh Series 



Edited by L, H. Bailey 

Carleton: The Small Grains. 

B. M. Duggar: The Physiology of Plant Produc- 
tion. 

/. F. Duggar: Southern Field Crops. 

Fisk: The Book of Ice-Cream. 

Gay: Breeds of Live-Stock. 

Gay: Principles and Practice of Judging Live- 
stock. 

Goff: Principles of Plant Culture. 

Guthrie: The Book of Butter. 

Harper: Animal Husbandry for Schools. 

Harris and Stewart: The Principles of Agronomy. 

Hitchcock: Texi^book of Grasses. 

Jeffery: Text-Book of Land Drainage. 

Jordan: Feeding of Animals. Revised. 

Livingston: Field Crop Production. 

Lyon: Soils and Fertilizers. 

Lyon, Fippin and Buckman: Soils : Their Properties 
AND Management. 

Mann: Beginnings in Agriculture. 

Montgomery: The Corn Crops. Revised. 

Morgan: Field Crops for the Cotton-Belt. 

Mumford: The Breeding of Animals. 

Piper: Forage Plants and Their Culture. 

Sampson: Effective Farming. 

Smith: Agricultural Meteorology, 

Thorn and Fisk: The Book of Cheese. 

Warren: Elements of Agriculture. 

Warren: Farm Management. 

Wheeler: Manures and Fertilizers. 

White: Principles of Floriculture. 

Widtsoe: Principles of Irrigation Practice. 



AGRICULTURAL 

METEOROLOGY 

THE EFFECT OF WEATHER ON CROPS 



J. WARREN SMITH, B.S.M.S. 

SPECIALIST IN WEATHER AND CROPS 



THE MACMILLAN COMPANY 
1920 

All rights reserved 






Copyright, 1920 
By the MACMILLAN COMPANY 



Set up and electrotypcd. Published December, 1920. 



DEC 15 192Q 
©C!.Ae05008 



PREFACE 

This book is designed primarily for university and college 
students, but it is entirely practicable for agricultural high- 
schools, and for farmers' reading-courses. It will prove of 
interest to individuals who wish information regarding cli- 
mate and crops, and the effect of the weather in varying the 
yield of crops. 

The text is the outgrowth of over thirty years in climate 
and crop work in different sections of the United States, and 
fifteen years contemporary instruction in meteorology and 
agricultural meteorology at the Ohio State University. 

The advanced students, especially, should use the avail- 
able references at the close of each, chapter. The instructor 
should extend the exercises and practicums, as the time avail- 
able will admit. Original investigations of the effect of 
weather on the yield of crops can be made very readily by 
following the outlined procedure. Published climatic data 
may be found for individual states by writing the State Sec- 
tion Director, United States Weather Bureau, or the Chief 
of the Weather Bureau at Washington, D. C. Crop yield 
data can be obtained from the State Departments of Agri- 
culture, or from the Bureau of Crop Estimates, Washington, 
D. C. 

As this is the first text on the subject of agricultural mete- 
orology that has ever been prepared, the author has had 
recourse to articles and papers by ecologists, botanists, plant 
physiologists and pathologists, entomologists, and the like. 
It has not been practicable to give the references in the text, 
but the literature at the close of each chapter indicates most 
of the articles that have been referred to. Charts that are 
not original or credited in the footnotes are from the publi- 
cations indicated in the references at the close of each chap- 
ter. 

We wish to give full credit to each author from whom in- 
formation has been obtained. It is desired also to give due 



VI 



PREFACE 



credit to various officials of the Weather Bureau whose papers 
and studies have been drawn on in the following pages. 

Some of the data were from- original studies made by 
the following-named students while taking the course in 
agricultural meteorology at the Ohio State University: 



H. N. Bunnell. 
Edward B. Scott. 
Paul Geiger. 
H. A. Stevens. 
Don C. Mote. • 
Earl Jones. 
C. E. Dike. 



Clark S. Wheeler. 
H. C. Hyatt. 
Ralph Kenny. 
Ernest N. Furgus. 
J. T. Burns. 
Dan L. Augenstine. 
C. F. Tom. 



Washington, D. C. 
May 1, 1920. 



J. WARREN SMITH. 



TABLE OF CONTENTS 

(Numbers in the text refer to paragraphs) 
CHAPTER I 

PAGES 

Introductory Meteorology ...... 1-22 

Weather, 1 ; Climate, 2. The Atmosphere: Composition, 
3; Nitrogen, 4; Oxygen, 5; Carbon dioxide, 6; Water- 
vapor, 7; Other gases, 8; Height of the atmosphere, 9. 
Pressure of the Atmosphere: Pressure varies with altitude, 
10; The barometer, 11; The barometer and weather fore- 
casting, 12. Temperature: Source of heat, 13 ; How the air 
is warmed, 14; Radiation, 15; How the air is cooled, 16; 
Inversion of temperature, 17; Diurnal range in tempera- 
ture, 18; Diurnal changes slight in cloudy weather, 19; 
Diurnal temperature changes greatest over land, 20; An- 
nual temperature ranges, 21 ; Adiabatic change in temper- 
ature, 22; The average vertical temperature gradient, 23; 
Recording the temperature, 24; Temperature records, 25; 
Mean temperature and vegetation, 26. Precipitation: 
Moisture in the atmosphere, 27; Depends on the tempera- 
ture, 28; Evaporation, 29; Humidity, 30; Relative humid- 
ity, 31; Saturation, 32; Dew-point, 33; Measuring the 
moisture in the atmosphere, 34; Condensation, 35; How 
clouds are formed, 36; Cloud types, 37; What makes it 
rain, 38 ; Rainfall increases with elevation on the windward 
side of mountains, 39; Measuring rainfall, 40; Rainfall 
data, 41; Snow, 42; Sleet, 43; Hail, 44; Dew, 45; Frost, 
46; Glaze, 47; Intensity of rain, 48; Rain-making, 49; 
Shooting hailstorms and tornados, 50. Circulation of the 
Atmosphere: What makes the wind blow, 51; Surface cur- 
rents, 52; General currents interrupted, 53; Most impor- 
tant interruptions outside of the doldrums due to high and 
low pressure areas, 54; Monsoon winds, 55; Land and sea 
breezes, 56; Mountain and valley winds, 57; Cold waves, 
58; Tornadoes and waterspouts, 59; The tornado tube, 
vii 



viii TABLE OF CONTENTS 

PAGES 

60; Where tornadoes occur, 61; Hurricanes, 62; A severe 
hurricane, 63; Other winds, 64; Wapm wave, 65; Blizzards, 
66; Hot winds, 67; Chinooks, 68; Measuring the wind 
velocity, 69; The pressure exerted by wind, 70; Estimating 
wind velocity, 71. 

CHAPTER II 

Agricultural Meteorology ...... 23-27 

Conditions for plant growth, 72; Factors must be in 
correct proportion, 73; Requirements vary, 74; Critical 
periods of growth, 75; To determine critical period, 76; 
Laboratory experiments, 77; Field observations, 78; Ob- 
servations in Russia, 79; Records in Canada, 80; Records 
in the United States, 81; Value of records, 82; Correla- 
tion of weather with past records of crop yields, 83 ; Not 
a new science, 84. 

CHAPTER III 

Agricultural Climatology ...... 28-33 

Climate and man, 85; In the Arctic, 86; In the tem- 
perate zone, 87; Native vegetation a key to field crops, 
88; Importance of temperature, 89; Seasonal develop- 
ment of crops, 90; Bioclimatic law of latitude, longitude, 
and altitude, 91; Local influences, 92; Practical applica- 
tion of law, 93; An aid in farm management, 94; Natural 
vegetation an aid in determining best dates for farm 
operations, 95; Phenological records desirable, 96; Rec- 
ords from simple meteorological instruments valuable, 
97. 

CHAPTER IV 

Correlation ........ 34-60 

A common method, 98; Relation of lines, 99; A better 
method, 100; Proper way to find the relation between 
two variables, 101 ; The dot chart the first step, 102; How 
dot chart is made, 103; Potato yield and temperature, 104; 
No relation shown in Fig. 15, 105; A negative relation in 
Fig. 14, 106; Fig. 13 indicates a positive relation, 107; 



TABLE OF CONTENTS ix 

PAGES 

When mathematical correlations should be made, 108; 
To determine the straight line of nearest fit, 109; Equa- 
tion for a straight line, 110; To determine values of a and 
b. 111; To locate line AB, 112; When a curve fits the 
data best, 113; Evaluation of the coefficients, 114; Least 
square method, 115; The equation for a parabola, 116; 
Star point method for calculating the parabolic curve, 
117; Star point method applied to other problems, 118; 
Accuracy necessary, 119; Calculating the parabolic curve, 
120; Normal equations, 121; Solving for unknown quan- 
tities, 122; Solving by direct solution, 123; To determine 
the value of y and x, 124; Checking the work, 125; The 
hygrometric equation for El Paso, Texas, 126; Practical 
application of the formula, 127; Other curves, 128; The 
correlation coefficient, 129; Definition and explanation, 
130; Most commonly used in showing relation between 
weather and crop yield, 131; How to calculate the cor- 
relation coefficient, 132; Explanation of table, 133; Aver- 
age corn yield, 134; Value of correlation coefficient, 135; 
The probable error, 136; Partial or net correlation, 137; 
A graphic illustration of the influence of two factors on a 
third, 138. 

CHAPTER V 

Climate and Crops ....... 61-100 

Solar or mathematical climate, 139; Physical or nat- 
ural climate, 140; Three classes of climate, 141; Conti- 
nental and marine climates, 142; Mountain climate, 143; 
Verdant zones or thermal belts, 144; Climatic zones, 145; 
Relative areas and limits, 146; The main factors in cli- 
mate, 147. Temperature: Importance, 148; Temperature 
effects, 149; Temperature and plant distribution, 150; 
Affects various plants differently, 151; Periods of growth, 
152; Periods of rest, 153; Length of rest period, 154; Ef- 
fective temperatures, 155; Temperature and carnations, 
156; "Zero " of vital temperature point 6° C. (42.8' F.), 
157; A new "zero" suggested, 158; Total effective tem- 
peratures, 159; Summation processes, 160; The remainder 
indices, 161; Exponential indices, 162; Physiological 



X TABLE OF CONTENTS 

PAGES 

summation indices, 163; Both temperature and moisture, 
164; Weakness of summation plan, 165; Plant tempera- 
tures, 166; Temperatures of leaves higher in sunshine 
than air temperatures, 167; Leaves cooler at night, 168; 
Effect of cloudiness on plant temperature, 169; Difficulty 
of comparing plant temperatures, 170; Leaf temperature 
fluctuation rapid, 171; Value of temperature summation 
figures, 172; Solution possible, 173; Lissner's law, 174; 
Lissner's aliquot, 175; Optimum conditions, 176; Time 
factor, 177. Soil Temperature: Most favorable tempera- 
ture, 178; Source of heat, 179; Loss of heat, 180; Diurnal 
changes in temperature, 181; The lag in temperature 
fluctuation, 182; Annual ranges, 183; Soil cover, 184; 
Snow cover, 185; Desirability of soil temperature records, 
186. Precipitation: Distribution of precipitation, 187; 
Precipitation in the United States, 188; Quantity of 
water, 189; Drought, 190; Rainfall and plant growth, 
191; Soil-moisture, 192; Wilting coefficient, 193; Tran- 
spiration, 194; Evaporation, 195; Evaporation and rain- 
fall, 196; Rainfall efficiency, 197; Evaporation from the 
soil, 198; Water requirement of plants, 199; Water re- 
quirement at different periods of growth, 200; Relative 
water requirements of plants, 201 ; Farming in the semi- 
arid regions, 202; Irrigation in humid districts, 203. 
Sunshine or Light: Clouds, 204; Solar energy, 205; Sun- 
shine-hour degree, 206; Variation with latitude, 207; The 
effect of light, 208; Different intensities, 209; The effect 
of sunshine, 210; Sunshine raises the temperature, 211; 
Sunshine sometimes unfavorable, 212; Sunshine for to- 
mato pollen, 213; Diffuse light, 214; Lack of knowledge, 
215; Knowledge of sunshine effect important, 216; Amer- 
ican Beauty rose, 217; Sunshine, temperature, and mois- 
ture, 218. Wind: Beneficial winds, 219; Damaging 
winds, 220. 

CHAPTER VI 

Climate and Farm Operations ..... 101-105 
Well-defined crop zones, 221 ; The southern subtropical 
coast, 222; The cotton-belt, 223; Corn and winter wheat 



TABLE OF CONTENTS 



XI 



PAGES 



belt, 224; The spring wheat belt, 225; The hay and pas- 
ture region, 226; The shifting of crop areas, 227; A change 
in farm operations, 228; Butter and cheese-making in 
Wisconsin, 229; Length of the growing season, 230; Cli- 
mate and the number of crops, 231; The double-cropping 
system, 232; The distribution of rain, 233; Rain and har- 
vesting dates, 234; Arid and semi-arid regions, 235; 
Larger farms necessary in drier regions, 236; Weather 
risk, 237; Spring frosts, 238. 



CHAPTER VII 

Weather and Crops ....... 

Weather variation effects relative, 239; Warm and 
cold season crops, 240; A complex problem, 241. Fiber 
Crops: Cotton: Climatic limits, 242; In the United States, 
243; Length of growing season, 244; Temperature and 
cotton, 245; Fall frosts damaging, 246; Temperature and 
the progress of ginning, 247; Rainfall and cotton, 248; 
Rainfall distribution important, 249; Heavy rainfall, 
250; Weather-cotton equation, 251; Equation in Texas, 
252; General weather effects, 253; Seasonal weather, 254; 
April, 255; May, 256; June, 257; July and August, 258; 
Rainfall in July and August not the controlling factor in 
Texas, 259; Winter rainfall and the yield of cotton in 
Texas, 260; Some important comparisons, 261; Septem- 
ber and October, 262; The weather effects of two seasons 
compared, 263; Insect pests, 264; Boll-weevil and tem- 
perature, 265; Boll-weevil and rainfall, 266; Wind and 
spread of weevil, 267; Flax: In North America, 268; Mois- 
ture and flax, 269; Frost effects, 270; Flax in North 
Dakota, 271; Hemp: In the United States, 272; Growing 
season, 273; Temperature, 274; Rainfall, 275; Fruits: Al- 
monds: Temperature and almonds, 276; Moisture and 
almonds, 277; Apples: Weather and apple jdeld, 278; 
February, 279; March, 280; Other months, 281; Fruit 
and leaf development, 282; Combined effect of June and 
February, 283; August and February combined, 284; 
Combined precipitation for June, August, and February, 
285; Apple diseases, 286; Codlin-moth, 287; Apricots, 



106-141 



Xii TABLE OF CONTENTS 

PAGES 

288; Avocado or alligator-pears, 289; Cherries: Weather 
and cherries, 290; Currants and gooseberries, 291; Cran- 
berries: Cranberries and temperature, 292; Protection 
from frost, 293; Dates, 294; Figs: Fig-growing, 295; 
Grapes: Temperature and grapes, 296; Critical tempera- 
tures, 297; Weather and grapes, 298; Sugar-content, 299; 
Olives: Temperature, 300; Peaches: Temperature effects, 
301; Critical temperatures in Missouri, 302; Tempera- 
ture and peach trees, 303; Moisture and peaches, 304; 
Weather and the yield of peaches, 305; Diseases of 
peaches, 306; Pears, 307; Plums: Plum trees, 308; Straw- 
berries: Moisture and strawberries, 309; Temperature 
effects, 310; Harvesting, 311; Adaptation to climate, 312; 
Strawberry diseases, 313; Citrus fruits: Oranges, 314; 
June drop of navel oranges, 315; Oranges in Florida, 316; 
Lemons, 317; Limes, 318; Pomelos, 319; Temperatures 
withstood: Critical frost temperatures for fruit, 320; Per- 
centage of damage, 321; Critical temperatures relative, 
322; Safe temperatures, 323; The orange tree, 324; 
Peaches, 325; Cranberries, 326; Dormant period, 327; 
Most susceptible period, 328; Weather and the setting of 
fruit, 329; Temperature effects, 330; The killing of plant 
tissue, 331; Frost is most damaging when fruit is wet, 
332; Sun-scald, 333. 

CHAPTER Vin 

The Effect of Weather on the Yield of Grains . . 142-214 
Barley: Range in the United States, 334; Temperature 
and barley, 335; Rainfall and barley, 336; Critical period 
of growth, 337; In Wisconsin, 338. Buckwheat: Weather 
and buckwheat, 339. Corn: Where grown, 340; In the 
United States, 341; Climatic factors, 342; Climatic limits, 
343; When planted, 344; Temperature and planting dates, 
345; Corn planting and average frost dates, 346; When 
harvested, 347; Length of the growing season of corn, 
348; Varieties and length of growing season, 349; Tem- 
perature and corn, 350; Growth and temperature, 351; 
Moisture and corn, 352; Transpiration and leaf area, 353; 
The moisture requirements of corn, 354; Best dates for 



TABLE OF CONTENTS xiii 

PAGES 

planting corn, 355; Measurements of water requirements 
vary, 356; The amount of dry matter, 357; Seasonal 
rainfall, 358; Rainfall and the yield of corn, 359; July 
rainfall and corn yield, 360; The two curves agree, 361; 
July rainfall and corn yield averages, 362; The four great- 
est corn states, 363; Comparisons close, 364; Striking 
averages, 365; Rainfall and temperature, and corn yield, 
366; Wet weather important, 367; Rainfall and corn 
yield averages, 368; Temperature effect not so impor- 
tant, 369; Combined rainfall and temperature effect, 
370; Average July rainfall and corn yields in Ohio, 371; 
Correlation for shorter periods than months, 372; August 
1 to 10 most important, 373; Thirty days from July 11 to 
August 10 most important, 374; Weather effects during 
different periods of development, 375; Thermal and rain- 
fall constants at Wauseon, Ohio, 376; The average date 
for planting corn, 377; Thermal constants and corn 
yield, Wauseon, Ohio, 378; Rainfall constants and corn 
yield, Wauseon, Ohio, 379; Rainfall near the blossoming 
time important, 380; Combined effect of rainfall and 
temperature, 381; Effective rainfalls, 382; Rainfalls of 
0.50 inch or more most effective, 383; Rainfall and corn 
in Tennessee, 384; The accumulated effect of the weather, 
385; W^eather and corn, 1918, 386; Spring frosts and corn, 
387; Fall frost damage, 388; Frost in 1917, 389; Freezing 
injury to seed corn, 390; Damage to seed corn in 1917, 
391; Short periods of drought and pollination, 392; Tem- 
perature and growth, 393; Drought and transpiration, 
394; Rate of seeding, 395; Weather and corn in the south 
temperate zone, 396. Oats: Range in United States, 397; 
Seeding and harvesting, 398; Winter oats, 399; Weather 
and oats in Portage County, Ohio, 400; In Wood County, 
Ohio, 401; For the state of Ohio, 402; In Indiana, 403; 
Illinois, 1878 to 1915, 404; Iowa, 405; Maryland, 406; 
North Dakota, 1892-1915, 407; Wisconsin, 408; Critical 
period for oats, 409; Weather and oats in Russia, 410; 
In England, 411. Rice: Rice districts in the United 
States, 412; Temperature and rice, 413; Water require- 
ment, 414. Rye: Range in the United States, 415; 
Weather and rye, 416; Rye in Wisconsin, 417. Grain 



XIV 



TABLE OF CONTENTS 



PAGES 



sorghums: Temperature and sorghums, 418; Range in 
the United States, 419. Wheat: Range, 420; In the 
United States, 421; Distribution as affected by tempera- 
ture, 422; Distribution as affected by moisture, 423; 
Dates of seeding and harvesting, 424; The best date to 
seed winter wheat, 425; Important periods of growth, 
426; Fruiting period, 427; Days from sowing to harvest- 
ing, 428; Critical periods of growth, 429; Moisture and 
wheat, 430; Weather and spring wheat, 431; Rainfall and 
spring wheat, 432; Temperature and spring wheat, 433; 
In North Dakota, 434; In South Dakota, 435; Weather 
and spring wheat, 436; Dry weather detrimental, 437; 
Weather and spring wheat in Manitoba, 438; Winter 
wheat : The effect of weather on the yield of winter wheat, 
439; Comparison of records in Ohio for fifty-four years, 
440; Precipitation and yield, 441; Temperature and 
yield, 442; Mean temperature for March, 443; March 
temperature in other states, 444; Effect of a snow cover, 
445; Snowfall as affecting wheat yield, 446; Snowfall in 
March detrimental, 447; In Indiana, 448; Cool and wet 
favorable in Indiana, 449; A cool May also beneficial in 
Indiana, 450; In Missouri, 451; May warm and dry most 
favorable in Missouri, 452; In Kansas, 453; Summer rain 
and yield of wheat in Kansas, 454; Rainfall and tempera- 
ture by months, 455; No temperature relation, 456; 
Rainfall and yield in Kansas, 457; July and April com- 
bined, 458; In Iowa, 459; In Wisconsin, 460; Winter- 
killing of grains, 461; Heaving, 462; Smothering, 463; 
Freezing of plants, 464; Physiological drought, 465; 
Winter wheat in 1919, 466; Yield disappointing, 467; 
Weather and hessian fly damage, 468; Rainfall and yield 
of wheat in Australia, 469; In Italy, 470; In England, 
471; Other factors should be studied, 472. 



CHAPTER IX 

The Effect of Weather on Vegetables and Miscella- 
neous Crops ........ 

Warm-weather crops, 473; Cool-weather crops, 474; 
Miscellaneous field and garden crops, 475; Planting dates, 



215-258 



TABLE OF CONTENTS xv 

PAGES 

476; White or "Irish" Potatoes; Range in the United 
States, 477; Planting and harvesting, 478; Temperature 
at beginning of planting, 479; Temperature requirements, 
480; Water requirement, 481; Distribution of water, 482; 
Weather and potatoes in Ohio, 483; Effect of varying 
rainfall, 484; Effect of temperature, 485; July most im- 
portant, 486; Some temperature and yield comparisons, 
487; Combined effect of temperature and rain, Ohio, 488; 
In New Jersey, 489; In Wisconsin, 490; In Michigan, 
491; In Licking County, Ohio, 492; In Portage County, 
Ohio, 493; Critical period of growth, 494; Correlation 
for short periods, 495; Diseases of potato plants, 496; 
Late blight, 497; Effect of temperature on late blight, 
498; Most favorable temperatures, 499; Temperature 
terms relative, 500; Time of development, 501. Hay and 
Forage Crops: Climatic factors, 502; Weather and yield of 
hay, 503; Hay in Ohio, 504; Hay in New York, 505; Hay 
in Wisconsin, 506; Hay in other states, 507; June rain, 
508; Alfalfa, 509; Alfalfa and temperature, 510; Alfalfa in 
Nevada, 511; Curing alfalfa, 512; Alfalfa seed and frost, 
513; Alfalfa seed warning service, Utah, 514; Clover, 
515; Weather and clover, 516; Clover in Ohio, 517; 
Clover seed, 518; Timothy, 519; Millet, 520; Sorgo, 521; 
Cowpeas, 522; Rape, 523. Sugar Products: Sugar-cane, 
524; Water requirements of sugar-cane, 525; Tempera- 
ture effects on sugar-cane, 526; Sugar-cane in the United 
States, 527; Sugar-beets, 528; Sugar-content of beets 
affected by temperature, 529; Sugar-beets as a winter 
crop, 530; Effects of rainfall on sugar-beets, 531; Tem- 
perature for sugar-beets, 532; Sunshine for sugar-beets, 
533; Correlation studies of sugar-beets, 534; Weather 
and maple products, 535; Weather and honey, 536; 
Temperature and honey, 537. Tobacco: In the United 
States, 538; Climate and tobacco, 539; Under shade, 540; 
Weather and tobacco, 541; In Kentucky, 542; In Ohio, 
543; Darke County, Ohio, 544; Montgomery County, 
Ohio, 1883 to 1908, 545; Southwestern Ohio, 546; Sum- 
mary, 547; Tobacco root-rot, 548. Seeds: Effect of 
weather on maturing seed, 549; Seeds from drier regions, 
550; Alfalfa seed, 551; Potato seed, 552; Wheat seed, 



XVI 



TABLE OF CONTENTS 



PAGES 



553; Regions especially favorable for seed, 554; Good 
"seed" weather, 555. Plant Diseases and Insect Damage: 
Terms relative, 556; Bitter-rot of apples, 557; Late blight 
of potatoes, 558; Wet weather diseases, 559; Dry weath- 
er diseases, 560; Grain rusts, 561; Spread by the wind, 
562; Smuts, 563; Insect damage, 564; Grasshoppers, 565; 
Chinch-bugs, 566; Temperature and chinch-bug, 567; 
Effect of wind on insects, 568; Cutworms, 569; White- 
grub, 570; Hessian fly, 571; Insect pests and parasites, 
572; Cattle-tick. 573. 



CHAPTER X 

Weather Forecasts and Warnings . . . . 

Forecast centers, 574; A. M. forecasts, 575; Value of 
forecasts, 576; Special forecasts for agricultural interests, 
577; P. M. forecasts, 578; Local forecasts, 579; Observa- 
tions, 580; Weather maps, 581; Weather laws, 582; 1st 
law: Weather moves eastward in temperate latitudes, 
583; 2nd law: The direction of surface winds depends on 
the difference in pressure, 584; 3rd law: The temperature 
^ at any place is largely controlled by the wind direction, 
585; 4th law: Pressure areas and weather, 586; Weather 
forecasts, 587; Special warnings, 588. Local Weather 
Signs: Humidity, 589; Good rain-indicators, 590; Mois- 
ture in vapor form, 591 ; Pressure of the atmosphere, 592; 
Wind and pressure, 593; Clouds, 594; High clouds, 595; 
Halos, 596; Low clouds, 597; Fog or mist, 598. Long- 
Range Forecasts: Seasonal forecast not yet possible, 599; 
Planets have no known effect on the weather, 600; Ani- 
mals, birds, and plants, 601. 



259-269 



CHAPTER XI 

Frost and the Protection of Crops from Frost Damage 
Average killing frost dates, 602; The growing season, 
603; Vegetative periods, 604; Comparison of the vegeta- 
tive with the frostless period, 605; The true growing 
season, 606; Extending the growing period, 607; When 
frosts occur, 608; Local conditions favorable for frost, 



270-282 



TABLE OF CONTENTS 



xvn 



609; Principles of frost protection, 610; Protection from 
frost damage by building fires, 611 ; Kinds of fuel, 612; Oil- 
heaters, 613; Oil consumed, 614; Kind of oil, 615; Light- 
ing heaters, 616; Cost of equipment, 617; Coal-heaters, 
618; Wood fires, 619; Great care needed, 620; Critical 
temperature, 621; The lowest temperature just before 
sunrise, 622; Protection by heating possible, 623. 



PAGES 



CHAPTER XII 

Value of Lightning-Rods ...... 

Thunder-storms, 624; Where thunder-storms occur, 
625; Nature of lightning, 626; Damage by lightning, 627; 
Loss by lightning greatest in rural districts, 628; Office of 
the lightning-rod, 629; Value of lightning-rods, 630; 
Lightning-rods as a protection to buildings, 631; Dam- 
age to rodded buildings, 632; Material for lightning-rods, 
633; Copper rods, 634; A continuous conductor necessary, 
635; Points above all projections, 636; Grounding the 
rods, 637; How spliced, 638; Care in installing, 639; Loss 
of live-stock, 640. 



283-292 



LIST OF ILLUSTRATIONS 

PLATES FACING PAGE 

I. — Cirrus clouds 11^ 

II. — Avection fog, with alto-stratus clouds above 27 "^ 

III. — Cumulus clouds 61 ^ 

IV. — Cumulo-nimbus cloud 77 ^ 

v.— The Hamilton oil-heater 139 ^ 

VI. — Oil-heaters in a grape orchard 155 ^ 

VII. — Heaters can be used successfully in protecting strawberries 

from frost damage 261 i/^ 

VIII. — (Upper) The California short-stack oil-heaters in place in an 
orange grove. (Lower) Improved taU-stack down-draft 
oil-heaters i)urning at night , 277 ^^ 

FIGURES PAGE 

1. — The mercurial barometer. This is the Fortin type, in most 

common use 3 

2. — Self-recording barometer or barograph 3 

3. — Examples of different states of air equilibrium 6 

4. — Maximum and minimum thermometers 7 

5. — Thermometers properly mounted in a lattice-work shelter ... 7 

6. — ^Richards thermograph, or self-recording thermometer 8 

7. — Sling psychrometer 10 

8. — Self-recording, tipping bucket rain-gage 12 

9. — Standard 8-inch rain-gage, with vertical cross section 13 

10. — Robinson's anemometer 19 

1 1 . — Relation of weather to the yield of potatoes in Ohio, 1883-1909 35 
12. — Relation of rainfall and temperature to the yield of potatoes 

in Ohio, 1883-1909 36 

13. — Dot chart showing the relation between the July rainfall and 

the yield of corn, Ohio, 1854-1913 38 

14. — Dot chart showing the relation between the mean temperature 

in July and the yield of potatoes, Ohio, 1860-1914 39 

15. — Dot chart showing the relation between the mean temperature 
in July and the yield of potatoes in Portage County, Ohio, 

1884-1913 40 

xix 



XX LIST OF ILLUSTRATIONS 

FIGURES PAGE 

16. — Dot chart showing the relation between the variation of the 
dew-point from the current temperature (the depression of 
the dew-point) at the evening observation, and the varia- 
tion of the minimum temperature from the evening dew- 
point. San Diego, California, radiation nights in Novem- 
ber from 1897-1916 42 

17. — Dot chart showing the relation between the evening relative 
humidity and the variation of the minimum temperature 
from the evening dew-point. El Paso, Texas, radiation 
nights in 1918 48 

18. — Chart showing the average time, in months, in which plant 

life in general remains more or less dormant 66 

19. — Graphs showing increase in value of index of temperature effi- 
ciency for plant growth (ordinates) with rise in tempera- 
ture itself (abscissas), for the three systems of indices. 
(From Livingston) 71 

20. — Chart of the United States showing climatic zonation accord- 
ing to remainder summation indices of temperature effi- 
ciency for plant growth, for the period of the average frost- 
less season. (Reproduced from Livingston and Livingston, 
1913) 73 

21. — Chart of the United States showing climatic zonation accord- 
ing to exponential summation indices of temperature effi- 
ciency for plant growth, for the period of the average frost- 
less season. (Reproduced from Livingston and Livingston, 
1913) 74 

22. — Chart of the United States showing climatic zonation accord- 
ing to physiological summation indices of temperature effi- 
ciency for plant growth, for the period of the average frost- 
less season, (Livingston) 75 

23. — Annual precipitation in the United States 81 

24. — Percentage of annual precipitation occurring between April 1 

and September 30 83 

25. — Cotton acreage in the United States in 1909. (Atlas of 
American Agriculture, Office of Farm Management, U. S. 
Department of Agriculture) 108 

26. — Average date when cotton planting begins. (Yearbook U. S. 

Department of Agriculture, 1917) 109 

27. — Average date when cotton picking begins. (Yearbook U. S. 

Department of Agriculture, 1917) 110 



LIST OF ILLUSTRATIONS Xxi 

FIGURES PAGE 

28. — Showing the relation of the mean temperature from May 1 
to June 30 and the amount of cotton ginned in Georgia and 
Alabama to September 25. (Kincer) 112 

29. — Relation between the rainfall in August and the yield of cotton 

in Texas, 1891 to 1918 , 117 

30. — Relation between the rainfall for July and August combined 

and the yield of cotton in Texas, 1891 to 1918 118 

31. — Relation between the rainfall from October to December and 
the yield of cotton in Texas during the following year, 1892 
to 1918 119 

32. — Relation between the rainfall from November to March and 

the yield of cotton in Texas the following fall, 1892 to 1918 120 

33. — Diagram showing the effect of the weather on the condition of 

cotton in Oklahoma in 1917 121 

34. — Diagram showing the effect of the weather on the condition 

of cotton in Oklahoma in 1918 122 

35. — Combined effect of the weather of June of the preceding year 
and February of the current year on the yield of apples, 
Belmont County, Ohio, 19 years 127 

36. — Combined effect of the weather for August of the preceding 
year and February of the current year on the yield of apples, 
Belmont County, Ohio, 19 years 129 

37. — Where corn is grown in the United States, (Yearbook, 

1915) : 145 

38. — Dates when corn planting begins. (Yearbook, 1917) 146 

39. — Mean daily temperature when corn planting begins in differ- 
ent parts of the United States east of the Rocky Mountains, 
and the dates on which these temperatures are reached . . . 147 

40. — Dates when the cutting and shocking of corn begins, in an 

average season. (Yearbook, 1917) 148 

41. — Relation between the rainfall for the month of July and the 

yield of corn in eight states, 1888-1915 152 

42. — Relation between the July rainfall and the yield of corn in 

four states, 1888-1915 154 

43. — Effect of July rainfall and temperature on the yield of corn, 

Ohio, 1854-1915 156 

44. — Relation between the July rainfall and the yield of corn in 

Tennessee, 1894-1908. (Voorhees) 168 

45. — Diagram showing the effect of the weather on the condition 

of corn in Iowa and Missouri in 1917 169 



xxii LIST OF ILLUSTRATIONS 

FIGURES PAGE 

46. — Diagram showing the effect of the weather on the condition 

of corn in Missouri in 1918 170 

47. — Where oats are grown in the United States. (Yearbook, 

1915) 174 

48. — ^Effect of the rainfall and temperature in June on the yield 

of oats in Illinois, 1876-1915 176 

49. — Winter wheat area in the United States. (Yearbook, 1915) . . 182 
50. — Spring wheat area in the United States. (Yearbook, 1915) . . 184 
51. — Average date when the seeding of spring wheat begins. 

(Yearbook, 1917) 186 

52. — Average date when the harvest of spring wheat begins. 

(Yearbook, 1917) 187 

53. — Average date when the seeding of winter wheat begins. 

(Yearbook, 1917) 188 

54. — Average date when the harvest of winter wheat begins in the 

United States. (Yearbook, 1917) 189 

55. — Date for seeding winter wheat which in a normal year will 

reduce or avoid injury by hessian fly and probably give a 

greater yield. (Yearbook, 1917) 190 

56. — Relation of rainfall in May and June to yield of spring wheat. 

North Dakota, 1891-1918 192 

57.— Relation of rainfall in May and June to yield of spring wheat. 

South Dakota, 1891-1918 193 

58. — Combined effect of the temperature for June and the rainfall 

for May and June on the yield of spring wheat in North 

Dakota, 1891-1913. (Blair) 194 

59. — Combined effect of the temperature for June and the rainfall 

for May and June on the yield of spring wheat in South 

Dakota, 1891-1913. (Blair) 195 

60. — Effect of weather on the condition of spring wheat in North 

Dakota and South Dakota in 1918 198 

61. — Relation between the mean temperature for March and the 

yield of winter wheat, Ohio, 1860 to 1915 201 

62. — Relation between the snowfall in March and the yield of winter 

wheat in Fulton County, Ohio, 1892-1914 203 

63. — Relation between the rainfall for July of one year and for 

April of the following spring and the yield of wheat for that 

season, Kansas, 1893-1917. (Lanning) 206 

64. — Diagram showing the effect of the weather on the condition of 

winter wheat in 1917-1918 210 



LIST OF ILLUSTRATIONS xxiii 

FIGURES PAGE 

65. — Graph giving relation between the winter rain and the yield 

of wheat in Australia, 1890 to 1915. (Richardson) 212 

66. — Planting zones for vegetables in the eastern half of the United 

States 220 

67. — Average dates when the planting of early potatoes begins. 

(Yearbook, 1917) 222 

68. — The beginning of the harvest of early potatoes. (Yearbook, 

1917) 223 

69. — The combined effect of the July temperature and rainfall on 

the yield of potatoes in Ohio, 1860 to 1915 227 

70. — Average highest mean daily temperature during the warmest 

part of the season 235 

71. — Relation between the rainfall in May and the yield of hay 

(not including clover) in Ohio, 1858 to 1909 237 

72. — The region apparently best adapted for the cultivation of 

sugar-beets 245 

73. — Average tracks of high and low pressure areas in the United 

States as they move from west to east 262 

74. — A typical winter storm Dec. 15, 1893, that is central over 

southern Iowa 263 

75. — The same storm twenty-four hours later, Dec. 16, 1893 264 

76. — ^Average dates of last killing frost in the spring 270 

77. — Average dates of the first killing frost in the fall 271 

78. — Average number of days between killing frosts 272 

79. — Average number of days that the frostless period is shorter 

than the vegetative period. (Kincer) 273 

80. — Daily weather map showing an area of high pressure with a 
cool wave in the Northwest that may be expected to over- 
spread Ohio in the next forty-eight hours with general 
frosts 274 

81. — The high pressure area as shown in Fig. 80 is spreading south- 
eastward and is causing frosts in Ohio 275 

82. — The same area twenty-four hours later. It overspreads Ohio 
and frosts are widespread. The temperature will rise grad- 
ually as the area moves eastward 276 

83. — Lard-pail type of oil-heater, and one of the first in- 
vented 277 

84. — A type of coal-heater that will hold about 18 pounds of soft 

coal. They will burn seven or eight hours 279 

85. — Wood piled for orchard heating 280 



xxiv LIST OF ILLUSTRATIONS 

FIGURES PAGE 

86. — Record made by a self-recording thermometer, May 11 to 18, 

1914, at Delaware, Ohio , 281 

87. — Lightning-rod on a small general barn. (Farmers' Bulletin, 

842) 290 

88. — Method of placing points and connecting rods on a farm-house 

to protect from lightning. (Farmers' Bulletin 842) 291 



AGRICULTURAL METEOROLOGY 



AGRICULTURAL METEOROLOGY 

CHAPTER I 

INTRODUCTORY METEOROLOGY 

Meteorology is a study of the phenomena of the atmos- 
phere and includes what is known as weather and climate. 

1. Weather is the condition of the atmosphere at a def- 
inite time. One may speak of the weather that prevailed 
last week or that is being experienced today. It includes 
all the phenomena of the air that surrounds us, such as 
pressure, temperature, moisture, wind, and the like. 

2. Climate deals with the averages and the extremes of 
the weather that prevail at any place. Thus it will be seen 
that weather relates to time and climate to location. 

THE ATMOSPHERE 

3. Composition. — The air is composed of a mixture of a 
number of gases and vapors that differ widely from one 
another. 

4. Nitrogen, which constitutes about 78 per cent of the 
volume of the atmosphere, is an inert gas; that is, it does 
not easily combine chemically with other elements, and by 
diluting the oxygen it diminishes the activity of combustion. 
In certain compounds it is an essential crop fertilizer. 

5. Oxygen comprises about 21 per cent by volume of the 
atmosphere. It unites readily with many other elements 
and forms a large proportion of the waters of the ocean and 
of the superficial rocks of the earth's crust. It supports 
combustion and is necessary to animal and plant life. 

6. Carbon dioxide is very essential to plant life, although 
it comprises only about 0.03 per cent of the air. Owing to 
its greater density, it may form such a large percentage of 
the air in wells, silos, and the like, as to cause death. 



2 AGRICULTURAL METEOROLOGY 

7. Water-vapor is of extreme importance but is the most 
variable component of the atmosphere. Its volume per- 
centage varies with the temperature, hence while it averages 
2.6 per cent at the equator it is only 0.2 per cent at 70° N. 
latitude, and decreases rapidly with elevation. 

8. Other gases. — Argon comprises nearly 1 per cent of the 
atmosphere while other permanent gases are hydrogen, 
krypton, neon, helium, and xenon, although in very small 
quantities. 

9. Height of the atmosphere. — One-half of the atmosphere 
is within 3.3 miles of the surface of the ocean; at an elevation 
of 6 miles it is not sufficient to support life; at 30 miles the 
pressure is only one six-thousandth that at sea level, while 
at 50 miles it is so thin as to be incapable of scattering per- 
ceptible amounts of sunlight. How far it extends above 
this is not known but observations of meteors show a suffi- 
cient gas, principally hydrogen, at elevations between 100 
and 188 miles to retard their speed and render them luminous. 

PRESSURE OF THE ATMOSPHERE 

While the variations in the pressure of the atmosphere at 
any point on the surface of the earth are insufficient to be 
appreciable to the senses, yet the pressure or weight of the 
air is highly important. It forces water to rise in a pump 
when the pressure of the air therein has been diminished 
by means of a piston; its horizontal variations give rise to 
winds that in turn modify the temperature, moisture, and 
the like, and its accurate observation over wide areas enables 
the forecasters to predict the coming weather changes with 
considerable success. 

10. Pressure varies with altitude. — The pressure of the 
atmosphere decreases with altitude at an approximate rate, 
through the first mile or so, of one inch on the barometer 
scale with each increase of 1000 feet in elevation. The 
exact rate of decrease, however, is less at increasing eleva- 
tions because of the smaller amount of air above, and as it 
varies with the temperature, humidity, and so on, the rate 
of decrease is in accordance with a complex logarithmic law. 
A knowledge of the density of the air is of great practical 
importance in connection with the flight of projectiles, the 
study of atmospheric phenomena, and aeronautics. 



INTRODUCTORY METEOROLOGY 



i 



The aviator is limited in the height to which he can fly 
by the decrease in density of the air and its effect on himself 
and the performance of his engines. Plant development is 
only slightly if at all affected by variations in pressure. 

11. The barometer. — Atmospheric pressure is usually 
measured in terms of the linear height of the niercury column 
corrected for temperature, gravity, and 
the like, in a tube closed at the upper 
end, which is exhausted of air, and open 
at the bottom. The mercurial barome- 
ter in most common use is the Fortin 
type as indicated by Fig. 1. As the mer- 
curial barometer is delicate and difficult 
to move without danger of breaking, 
the aneroid barometer is used for rough 
determinations of land elevations and 
the heights of balloons, kites, and aero- 
planes. Fig. 2 shows a self-recording 
barometer or barograph operating on 
the principle of the aneroid barometer. 
12. The barometer and weather fore- 



n 



Fig. 1.— The mer- 
curial barometer. 
This is the Fortin 
type, in most 
common use. 




Fig, 2. — Self-recording barometer 
or barograph. 



casting. — While a knowledge of the barometric pressure in 
different places is the most important factor in weather 
forecasting, a single barometer, without a knowledge of sur- 
rounding conditions, is of little value in weather predictions, 
except possibly for a short time in advance and particu- 
larly when the pressure is changing rapidly. (See Chap- 
ter X.) 



AGRICULTURAL METEOROLOGY 



TEMPERATURE 

The human system is more susceptible to changes in at- 
mospheric temperature than to those of any other meteoro- 
logical element. Plant development is also very responsive 
to temperature variations, as shown in Chapter V. 

13. Source of heat. — The sun is the ruler of the tempera- 
ture on the earth's surface as is well shown by the changes in 
temperature from equator to pole, from summer to winter, 
and from day to night. The radiant energy from the sun is 
termed insolation. 

14. How the air is warmed. — The surface of the earth 
and the objects upon it are warmed by direct insolation in 
daytime while the layers of air in contact with the earth are 
warmed by conduction. Surface air thus warmed is then 
carried up by convection and in turn warms other masses by 
mixture and conduction. In addition to this, a considerable 
amount of the solar radiation is directly absorbed by the 
more humid portions of the atmosphere. 

15. Radiation. — Clean dry air is warmed very little by 
insolation, which explains the well known warmth of direct 
sunshine on bright clear days, even while it may be cool in 
the shade. In hazy weather the sun does not seem so warm 
because some of its heat is absorbed and scattered by water- 
vapor, dust particles, and the like, which are present in the 
air. Some of the solar energy that reaches the surface of the 
earth is reflected while much more is absorbed and then re- 
radiated. Water-vapor absorbs this long wave-length ter- 
restrial radiation in much larger proportion than the short 
wave-length insolation. 

16. How the air is cooled. — At night when insolation is 
absent, the surface of the earth and objects upon it cool 
rapidly through loss of heat by terrestrial radiation, and the 
layers of air in contact with the earth lose heat to it by con- 
duction. As cool air is denser than warm, there is no con- 
vection; hence in still clear nights the air near the surface 
of the earth is considerably cooler than that imUiediately 
above. There is also some loss of heat by direct radiation 
from the air, especially when humid. 

17. Inversion of temperature. — In the daytime the tem- 
perature of the air usually decreases from the surface of the 



INTRODUCTORY METEOROLOGY 5 

earth upward for a mile or so, at an average rate of 2° to 3° (F) 
for each 1,000 feet in elevation. Under the conditions ex- 
plained in the preceding paragraph, however, this is re- 
versed, the temperature of the air then increasing from the 
surface of the ground upward for any distance from a few 
feet to several hundred, and sometimes several thousand. 
This is the condition called inversion of temperature, and 
explains the formation of frost in valleys when nearby hill- 
sides may be free from damage. 

18. Diurnal range in temperature. — The warmest part 
of the day occurs between 2 and 4 p. m. when the heating by 
insolation or incoming radiation from the sun is just balanced 
by that from outgoing terrestrial radiation and conduction. 
The lowest temperature is just before sunrise when insola- 
tion becomes equal to terrestrial radiation. Fig. 86 shows 
the diurnal march of temperature on days when under clear 
skies there are strong diurnal variations in temperature as 
well as on days when cloudy weather or an incoming cool 
wave prevents or entirely masks the usual diurnal tempera- 
ture range. 

19. Diurnal changes slight in cloudy weather. — When 
clouds prevail, a considerable part of the insolation is re- 
flected from the upper surface of the clouds, and the temper- 
ature rises but little at the surface of the earth. Cloudy 
weather at night intercepts terrestrial radiation, and there 
is a comparatively slight fall in the temperature of the sur- 
face of the ground and consequently of the air in contact with 
it. Hence frosts are not expected during cloudy weather. 

20. Diurnal temperature changes greatest over land. — 
Land surfaces warm up under insolation about four times 
as fast as water surfaces and also cool much more readily at 
night. Water surfaces reflect about 40 per cent of the inso- 
lation that reaches them while land surfaces reflect very 
little ; radiant energy penetrates many feet into the water 
and practically not at all into land; there is essentially no 
evaporation from dry land surfaces while a considerable part 
of the insolation absorbed by the surface of the water is used 
in evaporation and therefore becomes latent and does not 
raise its temperature; water that becomes heated may be 
moved horizontally or vertically by convection while there 
is no such movement in the land, and besides the specific 



6 AGRICULTURAL METEOROLOGY 

heat of water is about five times that of dry soil. As a result, 
land areas and the air immediately above warm much faster 
than water areas under insolation, and also cool much faster 
at night. 

21. Annual temperature ranges. — The interior of con- 
tinents is also warmer in summer and colder in winter than 
coast districts unless the water surfaces are covered by ice. 
On the leaward side of oceans, such as the Pacific coast where 
the winds blow quite persistently from the west, the annual 



temperature:, "c. 

^ , t S 3 4t 5 6 7 6 i 


> /O 1 


'alt. 

METERS 
500 

400 

300 

200 

100 

.r 


METSnS 

soo 

■400 
300 

zoo 

iOO 
























c 


\ 


\e 


\ 


V 
















\ 


\ 


\ 


\ 


\, 
















) 




\ 


^ 


\ 














/ 






\ 




'N 


\ 






o^ 


y 










i^ 






f 


V. 







Fig. 3. — Examples of different states of air equilibrium: AB, adiabatic 
gradient for dry air (neutral equilibrium) ; CD, temperature inversion 
(stable equilibrium), and EF, superadiabatic gradient (unstable 
equilibrium). 

range in temperature is much less than in the interior of the 
country or on the Atlantic coast. 

22. Adiabatic change in temperature. — Ascending air ex- 
pands and descending air is compressed because of the chang- 
ing pressure (see paragraph 10). When air is compressed 
work is done on it and its temperature is raised, when it ex- 
pands it does work and it is cooled. Whenever changes in 
pressure and volume of any gaseous matter occur without 
heat being added or subtracted from it, there will be a partic- 
ular rate of change of the temperature, depending on the 
nature of the gas. The rate of change is then called the adia- 



INTRODUCTORY METEOROLOGY 



batic rate. In the case of unsaturated air, the adiabatic rate 
of change of temperature amounts to 1.6° F. for each 300 
feet variation in elevation, or, more ac- 
curately, 1° C, for each 103 meters. 
The line AB in Fig. 3 illustrates the 
adiabatic gradient for dry air. 

23. The average vertical temperature 
gradient or rate of temperature change 
upward does not differ much during 
summer from the adiabatic gradient but 
does considerably in winter. When the 



Fig. 4. — Maximum (lower) 
and minimum (upper) 
thermometers. Instead 
of being set as in this il- 
lustration the minimum 
thermometer must be set 
level and the maximum 
thermometer with the 
bulb end slightly ele- 
vated, as is shown in 
Fig. 5. 




Fig. 5. — Thermometers properly 
mounted in a lattice-work shelter. 
The 8-inch rain-gage is shown set 
up in its shipping box at the right. 
(See Fig. 9.) 



surface of the ground and the air near it are warmed by 
bright sunshine, the line EF represents the gradient. The 
line CD represents the temperature variation under 



8 AGRICULTURAL METEOROLOGY 

conditions of temperature inversion as explained in para- 
graph 17. 

24. Recording the temperature. — The ordinary ther- 
mometer is well known. Fig. 4 illustrates the self-registering 
maximum and minimum thermometers and Fig. 5 these ther- 
moneters mounted in the louevered shelter in most common 
use. Thermometers must be exposed in the shade and so as 
to have good air ventilation. Fig. 6 shows a good type of self 
recording thermometer, or thermograph. 

25. Temperature records. — Maximum and minimum 
temperatures are important factors in crop development, as 
plants may be damaged by a few hours of excessive heat or 
killed by a brief period of freezing weather. The mean daily 
temperature is obtained approximately by adding the high- 
est and lowest temperature values together and dividing 
by 2. Similarly the mean monthly temperature may be ap- 
proximated by dividing the sum 
of the daily '^means'' by the 
number of days in the month. 

26. Mean temperature and 
vegetation. — Mean monthly 
temperature figures are usually 
given in climatological tables, 
but weekly or ten-day means 
are of more value in studying 
Fig. 6.— Richards thermograph, the relation between tempera- 
or self-recording thermometer, ture and plant growth.^ Mean 

maximum and mean minimum 
temperatures are often of more importance in vegetation 
than the mean daily temperatures because they represent 
more clearly the actual temperatures that plants experience. 

PRECIPITATION 

Dove has said: ''The atmosphere is a vast still, of which 
the sun is the furnace, and the sea the boiler, while the cool 
air of the upper atmosphere and of the temperate zones 
plays the part of condenser, and we on a wet day catch some 
of the liquid which distils over." 

27. Moisture in the atmosphere. — Water-vapor is one of 
the most important constituents of the atmosphere. It is 
essential to animal and vegetable life, and yet on a cold win- 




INTRODUCTORY METEOROLOGY 9 

ter day it may not comprise more than .001 part of the at- 
mosphere, and its maximum on a warm summer day near the 
seashore is never more than about .05 of the atmosphere. 

28. Depends on the temperature. — The temperature de- 
termines the amount of invisible moisture that can be present 
in the atmosphere as is shown by the following, giving the 
weight of water vapor in the atmosphere when completely 
saturated : Weight of a cubic foot 

Temperature of saturated vapor. 

degrees F. Grains troy 

100 19.766 

80 10.933 

60 5.744 

40 2.849 

20 1.235 

0.481 

-10 0.285 

-20 0.166 

-40 0.050 

This indicates that at a temperature of 40° it is not possible 
for the air to contain more than one-half as much water- 
vapor as it can at 60°. Almost one-half of the total water- 
vapor in the whole envelope of air that surrounds the earth is 
within one mile of the earth's surface, while one-half of the 
atmosphere is above three and one-third miles. 

At a height of six miles above the surface of the earth, 
where the temperature is about 60° below zero, the total 
amount of water-vapor is only one ten-thousandth of the 
atmosphere. 

29. Evaporation. — The process by which a liquid becomes 
a gas or vapor is termed evaporation. The rate of evapor- 
ation or the rapidity of the escape of the molecules from the 
water surface into the atmosphere in the form of vapor de- 
pends on the temperature, wind velocity, dryness of the 
air, and to a slight extent the pressure. 

30. Humidity. — The amount of water-vapor present in 
the atmosphere is called the absolute humidity, and it may 
be expressed in the weight of the vapor in a unit volume, 
or in the expansive force that the vapor exerts termed va- 
por pressure. The absolute humidity usually varies with 
the temperature. 



10 



AGRICULTURAL METEOROLOGY 



31. Relative humidity. — The absolute humidity divided 
by the saturation humidity at the same temperature is 
called the relative humidity. It- is expressed in percentages. 
The diurnal relative humidity curve varies inversely as the 
temperature. 

32. Saturation. — When the water-vapor present in the 
air is one-half as much as possible at the temperature, the 
relative humidity is said to be 50 per cent. When three- 
fourths, the relative humidity is 75 per cent. When the 
relative humidity is 100 per cent, the air is said to be com- 
pletely saturated. 

A room 20 x 20 feet and 10 feet high contains 4,000 cubic 
feet of air. If this air were completely saturated at a tem- 
perature of 80°, there would be 3 quarts of water in the at- 
mosphere in an invisible form. If the tem- 
(Iw^ perature should be 60°, only 3 pints of water 

i^^=rii could be held in suspension in the atmos- 
I im phere of the room. If the temperature of 

I 1^ the air should be zero, it could contain less 

I w| than 0.3 of a pint of water. 

II |[Bk 33. Dew-point. — The dew-point is the 
it MS temperature of saturation for the moisture 
IJl mH present. During the warmest part of the 

III ^^ (Jay, while the actual amount of moisture in 
the atmosphere is usually large, the amount 
is seldom sufficient for saturation, and the 
relative humidity is generally low. As the 
temperature falls in the late afternoon, the 
capacity for moisture decreases, hence the 
relative humidity increases. When satura- 
tion is reached, the temperature is at the 
dew-point. Any further cooling will cause 
part of the moisture to condense in the form 

of dew, fog, frost, or cloud. The difference 
between the temperature of the air and the 
dew-point temperature is called the com- 
plement or depression of the dew-point. 
34. Measuring the moisture in the at- 
mosphere. — The sling-psychrometer or whirled psychrometer 
is used to determine the dry and wet bulb temperatures (see 
Fig. 7). From these data and simple hygrometric tables, the 



F I G. 7. — S ling 
psychrometer. 



INTRODUCTORY METEOROLOGY 11 

absolute and relative humidity and dew-point temperature 
can easily be determined. 

35. Condensation. — The natural processes of the con- 
densation of the water-vapor in the atmosphere into visible 
form depend on a decrease in temperature. If the tempera- 
ture of the air in a room is at 80° and if the space is completely 
saturated, about one-half of the moisture would be forced to 
condense if the temperature should be lowered to 60°. The 
condensation of the moisture would take place upon the cloth- 
ing and other objects in the room which might be cold. The 
sweating of ice pitchers is a well known example of the con- 
densation of moisture upon any object the temperature of 
which is below the dew-point. 

36. How clouds are formed. — The temperature of the 
air is cooled sufficiently to cause the condensation of the sur- 
plus moisture into fog or cloud: (1) by expansional or dy- 
namic cooling due usually to vertical convection; (2) by 
contact cooling; (3) by the mixture of masses of air of un- 
equal temperatures; (4) by radiation. 

37. Cloud types. — There are three main cloud types. 
(1) Cirrus, very high fibrous, white clouds that are composed 
of ice particles (see Plate I). (2) Stratus, a low, fog-like 
cloud of wide extent. From the top of high elevations these 
clouds have the appearance of valley fogs (Plate II). (3) 
Cumulus, a flat-bottomed cloud with rounded top (Plate III). 
The cumulus is a typical fair weather cloud, but will fre- 
quently grow into the cumulo-nimbus or thunder head, as 
shown by Plate IV. There are many combinations of these 
cloud types some of which are very beautiful. A nimbus is 
any cloud from which rain is falling. This is frequently 
classified as a fourth cloud type. 

38. What makes it rain. — Rain is caused whenever a 
large mass of air is cooled below its dew-point or tempera- 
ture of complete saturation. Clouds are formed just as soon 
as the dew-point is passed and condensation into visible 
drops begins to take place. If the cooling continues, large 
drops will be formed from the smaller cloud particles and 
these drops will fall to the earth as rain. 

Vigorous cooling in masses of air of sufficient quantity to 
cause any considerable amount of precipitation is brought 
about only when the air is cooled by expansion. Wlien a 



12 



AGRICULTURAL METEOROLOGY 



mass of air is carried to higher altitudes by any cause it ex- 
pands, because there is less air above it and the presure on 
it is less and this act of expansion reduces its temperature. 
The rate at which it cools, before it reaches the tempera- 
ture of complete saturation, is 1° F. for every 188 feet. After 
condensation begins, the rate of cooling is considerably less. 
If a current of air with a temperature of 80° and a relative 
humidity of 75 per cent is forced up to ten times 188 feet, or 
but little more than one-third of a mile, some of the moisture 
must be condensed into clouds and rain. 

Ascending air is cooling and is then apt to be cloudy and 
rainy; descending currents of air are warming, the capacity 
for moisture is increasing instead of decreasing, and they are 
most likely to be accompanied by clear skies. 

39. Rainfall increases with elevation on the windward 
side of mountains. — Currents of air blowing over a range 
of mountains are being cooled by expansion at the adiabatic 
rate, and the temperature is decreasing, hence there will be 
an increase in the rainfall up to a certain level, depending on 
the topography, and the like. The maximum level is 
about 5,000 feet in the western mountains, but it varies in 
different places. Precipitation decreases 
with higher elevations on the windward 
side, and then decreases with decreasing 
elevation on the leaward side, as the air 
there is being warmed by compression. 

40. Measuring rainfall. — Fig. 8 shows 
one type of self-recording rain-gage, while 
Fig. 9 illustrates the ordinary rain-gage 
with a cross-section to show the different 
parts. The receiver of the standard 
(United States) is 8 inches in diameter, 
while the area of the inner tube is one- 
tenth of that of the catching surface. 
The amount of fall is measured, on a scale 
of 1 to 10, with an ordinary rule. That 
is, 1 inch of water in the gage is 0.10 
inches on the surface of the land, and so 
on. Amounts less than 0.01 inch (0.1 on the rule) are re- 
corded as ''T" (trace), an amount too small to be measured. 
41. Rainfall data. — Rainfalls are tabulated by daily, 




Fig. 8.— Self-record- 
ing, tipping bucket 
rain-gage. 



INTRODUCTORY METEOROLOGY 



13 



monthly, seasonal, and annual amounts, and long-period 
averages of these. The National Weather and Crop Bulle- 
tin published by the Weather Bureau shows weekly rainfall 
charts or tables. From an agricultural point of view, all pre- 



Frant Viexv. 



VerticaZ SecUaru 




HortzomixH S>ectzaw,E-F. 



O f i 3 4 S 6 7 8 9/0 // /2_J3 /4IS '617/ 8 ^3 £0 21 2223 <y INCHES. 
SCALE., 

Fia. 9. — Standard 8-inch rain-gage, with vortical cross-section. 

cipitation data should be tabulated and published in weekly 
or ten-day periods. 

42. Snow is composed of tabular or columnar particles 
of ice formed in the free air at temperatures below freezing. 
All are hexagonal in form but of endless variety in detail. 
The amount of water from snow averages about 1 inch for 
every 10 inches of snow. 

43. Sleet is composed of ice pellets, or frozen rain-drops 
(or largely melted snowflakes refrozen) due to the falling of 



14 AGRICULTURAL METEOROLOGY 

precipitation through a cold layer of air near the surface of 
the earth. Sleet occurs only during cold weather. 

44. Hail. — Lumps of ice more or less irregular in out- 
line, generally consisting of concentric layers of clearish ice 
and compact snow, are designated as hail. As defined by the 
Weather Bureau, hail can occur only in connection with 
thunder-storms, hence will rarely be seen and then only in 
warm weather. Sometimes hailstones are found as large as 
a base-ball, or again of the size and shape of saucers. 

45. Dew is water that has condensed on objects the 
teinperature of which is below the current dew-point of the 
air that is in contact with them. The cooling necessary for 
the formation of dew is usually due to the loss of heat by 
radiation. 

46. Frost is a light feathery deposit of ice caused by the 
same process that produces dew, but occuring when the tem- 
perature of objects on which it forms is below freezing. 

47. Glaze (ice storm) is a coating of clear smooth ice 
on the ground, trees, and so on. It is usually caused by 
rain falling on objects that have a temperature below 
freezing. 

48. Intensity of rain. — It makes considerable difference 
in the growth of crops, whether the rainfall is in the form of 
a few heavy downpours or whether it comes in frequent light, 
showers. Most climatological tables show the number of 
days with a rainfall or 0.01 inch or more, and the rainfall in- 
tensity can be determined by dividing the total weekly or 
monthly fall by the number of rainy days. It would be an 
excellent plan if the number of days with 0.25 inch or more 
were also given in the tables. 

49. Rain-making. — It has been held by many that it is 
possible to produce rain at will, and rain-making fakers have 
sometimes reaped rich harvests during periods of serious 
drought. It can be stated, however, that the processes of na- 
ture in producing rain are on far too large a scale to be du- 
plicated in the slightest degree by man and that it is abso- 
lutely impossible for man to produce an appreciable rain- 
fall in the open air over a considerable area. For example, 
the rainfall in Europe during the late war was only about 
normal notwithstanding the most terrific cannonading and 
bombing that the world ever saw. 



INTRODUCTOBJ METEOROLOGY 15 

50. Shooting hail-storms and tornados. — Some irrational 
speculations die hard and there are persons and communities 
in Europe and probably in this country that still believe it 
is possible to prevent hail and tornado damage by bombing 
the approaching storm cloud. Here again the forces of na- 
ture are too large to be dissipated by man-made efforts. 
Careful inquiries by capable men in France and elsewhere 
have failed to show any effect of hail firing whatever, but 
that the hail-storms continue to occur and that hail falls upon 
the "protected" and unprotected alike. 

CIRCULATION OF THE ATMOSPHERE 

If there is a difference in the temperature of the masses of 
air over two adjoining regions, there will be, through the ac- 
tion of gravity because of the resulting difference in pressure, 
a continuous overflow of air from the warmer to the "colder 
region, and an underflow from the colder to the warmer. 

51. What makes the wind blow. — Movements of the at- 
mosphere, or winds, are due to differences in pressure, caused 
by difference in temperature and modified by the rotation of 
the earth. 

52. Surface currents. — The large general movements of 
the atmosphere at the surface of the earth are: (1) The so- 
called doldrums or equatorial calms which surround the 
earth at the heat equator, where there are strong ascending 
currents; (2) the trade-winds which blow toward the warm 
equatorial belt, from a northeasterly direction in the nor- 
thern hemisphere and a southeasterly direction in the south- 
ern hemisphere, from about latitude 30°; (3) the "horse lat- 
itudes", or areas of partial calms at about latitude 30°, where 
there is an apparently well-defined descending current; (4) 
the prevailing westerlies which occur in temperate latitudes 
north of about latitude 25° to 30° in the Northern, and south 
of about latitude 25° to 30° in the Southern Hemisphere. 

53. General currents interrupted. — All these general 
currents are interrupted or confused by the differences in 
temperature which occur over large land and water areas; 
by seasonal variations in temperature; and by storms or 
other local disturbances. 

54. Most important interruptions outside of the doldrums 
due to high and low pressure areas. — In temperate lati- 



16 AGRICULTURAL METEOROLOGY 

tudes there is a constant succession of high and low pressure 
areas known, respectively, as anticyclones and cyclones 
which Inove in a west to east direction. As seen in Chapter 
X, the surface winds blow diagonally away from areas of 
high pressure and diagonally toward areas of low pressure. 

55. Monsoon winds. — Another marked interruption of 
the general currents is due to the temperature contrast be- 
tween large land and water areas. The land is warmer than 
the water jn the summer and colder in winter, and as a result 
there is a movement of the air from the colder toward the 
warmer of the two adjacent areas. Monsoon winds are, 
therefore, seasonal winds. 

56. Land and sea breezes. — Contrasted with the sea- 
sonal monsoons which prevail over large areas, there is a 
daily movement of the air over narrow areas along sea-coasts 
called land and sea breezes. The air along the coast flows 
toward the land in the daytime and toward the water at night. 
The sea breeze is felt for only a few miles, inland but it fur- 
nishes a pleasant relief from the heat where it does occur. 

57. Mountain and valley winds. — In some mountain 
regions, there is a well-defined movement up the valleys in 
the daytime and an even more marked movement down the 
valleys at night. 

58. Cold waves. — When a well-defined and energetic 
cyclonic area moves eastward across the central Mississippi 
Valley and the Great Lakes, strong southerly winds to the 
south and east of the center will cause unseasonably high 
temperatures, especially in winter time. With the shift of 
wind to west and northwest, as the center of disturbance 
moves eastward, the tetnperature falls rapidly. When the 
approaching high is large and well-defined, the northwest 
winds, often accompanied by snow squalls, are strong and the 
fall in temperature in twenty-four hours sometimes amounts 
to 40° or 50° or even more. These are the conditions which 
make up the well-known winter cold wave of the United 
States. After the windy front of the anticyclone has passed 
and the center lies over a district, the nighttime temperatures 
will be very low, especially in the valleys, under the influence 
of radiation and local surface "air drainage." 

59. Tornadoes and waterspouts. — The tornado is the most 
diminutive and yet the most violent and destructive of all 



INTRODUCTORY METEOROLOGY 17 

storms. It may be defined as a violent wind-storm accom- 
panied by hail, thunder, and lightning, in which the air masses 
whirl with great velocity about a central core while the whole 
storm travels across the country in a narrow path at a con- 
siderable speed. When seen from a distance, the tornado has 
the appearance of a dense cloud mass, usually in violent agita- 
tion and with one or more pendant funnel-shaped clouds 
which may or may not reach the earth. Waterspouts are 
tornadoes that occur over bodies of water. The visible water- 
spout corresponds to the pendant cloud of the land tornado. 

60. The tornado tube. — The tornado tube in its projec- 
tion downward from the cloud mass is a simple vortex and 
obeys the laws of fluids in gyratory motion. A partial vacuum 
is produced at the center of the whirl, the low temperature 
which results generates the sheath of vapor that makes the 
tube visible and the wind about the vortex prostrates every 
obstacle. Neither the air pressure nor the wind velocity have 
ever been measured near the center of a tornado but from 
the force necessary to move certain objects it has been cal- 
culated that the wind must blow at the rate of well over 100 
miles an hour and may reach a velocity of several hundred 
miles an hour. 

61. Where tornadoes occur. — The region of greatest fre- 
quency of tornadoes is the central plains states and the Miss- 
issippi Valley, where they occur most often in April and May. 
They may occur in the Gulf states in the winter or early 
spring, and in the northern states in su,mjner. The southern 
margin of a tornado is more dangerous than the northern, 
and as the width of the path of greatest destruction may not 
be more than a few yards or rods, a person can frequently 
find safety by running toward the northwest, if the tornado 
seems to be approaching directly. 

62. Hurricanes. — Most of the cyclonic storms which gain 
such a velocity of gyration as to constitute hurricanes origi- 
nate within the tropics. Those originating north of the 
equator m.ove northwestward, many reaching latitude 20° or 
more and then recurving toward the northeast. Those of the 
Southern Hemisphere first move southwestward, and later, 
in many cases recurve towards the southeast. Hurricanes 
are the most destructive of all storms. They have all the 
characteristics of tornados but instead of being a few rods 



18 AGRICULTURAL METEOROLOGY 

in width, their path of destruction may cover several hun- 
dred miles, and instead of their duration being less than one 
minute, as is the case with tornadoes, the terrific winds and 
rain accompanying them may last from twelve to twenty- 
four hours. Hurricanes seldom occur in the Northern Hem- 
isphere except in the late summer or early autumn. Although 
there are an average of about ten annually that touch some 
portion of the Atlantic or Gulf coast, an average of less than 
one a year is severely destructive. 

63. A severe hurricane. — The most intense hurricane of 
which there is record in the history of the coast of the Gulf 
of Mexico, and probably in the United States, moved into the 
lower Mississippi Valley on September 29, 1915. The pres- 
sure fell to 28.11 inches at New Orleans at 5.50 p. m., on the 
29th. The wind reached a five-minute velocity of 86 miles 
an hour from the southeast at 5.10 p. m., on the 29th. The 
extreme velocity was 130 miles an hour. At Burrwood, 
Louisiana, 100 miles south of New Orleans, the velocity was 
the highest ever recorded on the Gulf Coast. At Burrwood, 
the extreme wind for one minute was 140 miles an hour, at 
3.45 p. M., the maximum five-minute velocity was 124 miles 
an hour, and from 3.31 to 3.50 p. m., the average velocity was 
116 miles an hour. From 3.00 to 4.00 p. m., the average 
velocity was 108 miles an hour; from 4.00 to 5.00 p. m., 
106 miles an hour; and from 5.00 to 6.00 p. m., 96 miles an 
hour. The total loss of life in 300 miles of coast line was only 
275. Twenty-three of these fatalities were known to be due 
to an absolute disregard of warnings at Rigolets. The prop- 
erty loss was probably more than $13,000,000. At Leeville, 
of the 100 houses in the village, only one was left standing. 

64. Other winds. — Other winds of considerable interest 
in the United States are the ''warm wave,'' the ''blizzard," 
the "hot winds" of the Great Plains, and the"chinook." 

65. Warm wave. — This is a moisture-laden wind that 
blows from the south into an advancing cyclonic or low pres- 
sure area. It is particularly well-marked in the winter time 
in the central and eastern states, when almost summer heat 
may be experienced. The Italian name "sirocco" is some- 
times given this wind. 

66. Blizzards. — The blizzard is characteristic of the Great 
Plains and is a very strong, cold wind accompanied by fine 



INTRODUCTORY METEOROLOGY 



19 



snow or ice particles. Its onset is sometimes accompanied 
by a drop in temperature of 30° to even 60° in a few hours. 
Blizzards frequently cause great loss of stock and sometimes 
of human lives. 

67. Hot winds. — During long dry spells over the Great 
Plains, marked hot winds occur which cause great damage, 
particularly to corn. While they prevail, the transpiration 
is far greater than the moisture the roots can supply from 
soil that has already been depleted, and corn is frequently 
ruined over considerable areas. These winds sometimes 
occur at night and are so hot that persons are aroused with 
the belief that a fire is near. 

68. Chinooks. — The chinook occurs mainly on the east- 
ern side of the Rocky Mountains particularly in Montana 
and Wyoming, but may be felt in any mountain region. It 
is a hot dry wind which usually makes its appearance sud- 
denly and may raise the temperature by 40° to 50° F. in a 
few minutes. Chinooks are locally known as ''snow eaters" 
as the snow evaporates very rapidly and large areas previ- 
ously snow-covered are made available for grazing. The 
name ''chinook" is a local American 
term for a widespread type of wind to 
which the generic name " foehn " is ap- 
plied by meteorologists. Its warmth 
is due to the dynamic heating of a 
mass of air that is rapidly descending 
from a considerable elevation. 

69. Measuring the wind velocity. 
— Wind velocity is measured by 
means of a pressure-gage or most 
usually in the United States by a 
rotation anemometer as seen in 
Fig. 10. This will show by means of 
a dial the total wind movement for 
any short period of time, while by 
the use of a registering apparatus the 
time that it takes each mile of wind to 
pass the point is recorded. The 
"maximum" wind as reported by the Weather Bureau is the 
greatest number of miles recorded in five minutes of time. 
The extreme velocity is the quickest time for any single mile. 




Fia. 10. — Robinson's ane- 
mometer. The cups 
rotate at a rate ap- 
proximately one-third 
that of the wind. 



20 AGRICULTURAL METEOROLOGY 

The cups in the Robinson's anemometer are 4 inches in 
diameter while the supporting arms are 6.72 inches long. 
With these dimensions the cups move at approximately one- 
third the velocity of the wind. One mile of wind will cause 
500 revolutions of the cups. 

70. The pressure exerted by wind. — Within a range in- 
dicated approximately by velocities of 3 and 50 meters a 
second (63^ and 112 miles an hour), the pressure of the wind 
varies nearly as the square of the velocity. In any instance 
the actual pressure also depends on the character and di- 
mensions of the surface and the density of the air which, in 
turn, is a function of the barometric pressure and the tem- 
perature of the air. At sea-level, under ordinary conditions, 
wind-pressures may be determined with fair accuracy by the 
formula, — 

P = 0.0735 SV2 

in which P is the pressure in kilograms to the square meter of 
surface exposed normal to the wind, S the surface in square 
meters, V the velocity in meters a second, and 0.0735 a fac- 
tor determined by experiment. 

The following indicates the pressure corresponding to the 
velocity of the wind as recorded by the Weather Bureau anem- 
ometers : 



dicated wind velocity 


Wind pressure; pounds 


in miles per 


hour 


per square foot 


10 




0.369 


20 




1.27 


30 




2.64 


40 




4.44 


60 




6.66 


60 




9.22 


70 




12.2 


80 




15.5 


90 




19.2 



71. Estimating wind velocity. — When no instruments are 
available for measuring the wind velocity, as is generally the 
case at sea, it may be estimated approximately by means of 
the following scale, which is the Beaufort or standard scale 
in most common use : 



INTRODUCTORY METEOROLOGY 



21 



Beaufort Explanatory 
number titles 



Miles per 
hour 



Apparent effect 





1 


Calm 
Light air 


Less than 1 
1 to 3 


2 


Slight breeze 


4 to 7 


3 


Gentle 
breeze 


8 to 12 


4 
5 


Moderate 
breeze 
Fresh breeze 


13 to 18 
19 to 24 


6 


Strong 
breeze 


25 to 31 



7 High wind 32 to 38 

8 Gale 39 to 46 

9 Strong gale 47 to 54 

10 Whole gale 55 to 63 

U Storm 64 to 75 

12 Hurricane Above 75 



Calm, smoke rises vertically. 

Direction of wind shown by 
smoke drift, but not by wind 
vanes. 

Wind felt on face; leaves rustle; 
ordinary vane moved by wind. 

Leaves and small twigs in con- 
stant motion; wind extends 
light flag. 

Raises dust and loose paper; 
small branches are moved. 

Small trees in leaf begin to 
sway; crested wavelets form on 
inland waters. 

Large branches in motion; whis- 
tling heard in telegraph wires; 
umbrellas used with difficulty. 

Whole trees in motion; incon- 
venience felt when walking 
against wind. 

Breaks twigs off trees; generally 
impedes progress. 

Slight structural damage occurs 
(chimney pots and slate re- 
moved) . 

Seldom experienced inland; 
trees uprooted ; considerable 
structural damage occurs. 

Very rarely experienced, accom- 
panied by widespread damage. 



LABORATORY EXERCISES 

1. Paragraph 6. By expelling the breath into a tall drinking glass 
and then inserting a lighted match, the effect of the excess of carbon 
dioxide and the lack of oxygen will be seen. One should never go into 
an old well or deep cistern or a partially filled silo without first lowering 
a candle or lantern into it. If the light is extinguished, there is a dan- 
gerous excess of carbon dioxide. 

2. Paragraph 10. Determine the variation in pressure at different 
elevations by means of an aneroid barometer. A deUcately adjusted 



22 AGRICULTURAL METEOROLOGY 

instrument will show a difference in pressure between the floor and the 
top of an ordinary table. 

3. Paragraph 15. Expose one therrnometer to direct sunshine, and 
another near the first, but shaded from the sun. 

4. Paragraph 17. Obtain temperature at different elevations on 
clear still nights. 

5. Paragraph 18. Study the records from a thermograph in clear 
weather as compared with cloudy weather, (par. 19) 

6. Paragraph 24. Observations should be made with thermometers 
properlj'' exposed. 

7. Paragraph 34. Determine absolute and relative humidity and 
dew-point with a sling psychrometer. 

8. Paragraph 37. The main cloud types should be learned. 

9. Paragraph 71. Practise estimating the wind velocity wherever 
anemometer records are available to verify the estimates. 

REFERENCES 

Physics of the Atmosphere. Wm. J. Humphreys. Franklin Institute, 
1920. 

Introductory Meteorology. Yale University Press, 1918. 

Climate. R. DeC. Ward. G. P. Putnam's Sons. (2d edition), 1918. 

Meteorology. W. I. Milham. The Macmillan Co. 1912. 

Descriptive Meteorology. W. L. Moore. D. Appleton & Co., 1910. 

Handbook of Climatology. Dr. Julius Hann. Translated, with ad- 
ditional references and notes by R. DeC. Ward. The Macmillan 
Co., 1903. 

Elementary Meteorology. Wm. M. Davis. Ginn & Co., 1894. 

Monthly Weather Review, with Supplements; National Weather and 
Crop Bulletins; Climatological Data for the United States, by Sec- 
tions, and miscellaneous reports by theU. S. Weather Bureau, con- 
tain important statistical data and articles on the general subject 
of meteorology. 



CHAPTER II 

AGRICULTURAL METEOROLOGY 

Agricultural meteorology may be defined as "meteorology 
in its relation to agriculture." It considers the vegetation 
and animal life of the globe, the distribution of food and 
other crops, and farm operations as afTected by climate. It 
shows the effect of weather on the growth and yield of crops. 
It treats of the influence of climate and weather on insect 
activities, the development of plant diseases, and the pro- 
tection of crops, animal life, and buildings from damaging 
meteorological phenomena. 

72. Conditions for plant growth.— There is an optimum 
combination of temperature, moisture, and sunshine in which 
plants make their best growth, and under which the largest 
yields will be obtained. Food is available to the roots of 
plants only in a soluble form ; it is carried into the plants and 
converted into vegetable tissue under the influence of solar 
energy expressed in heat units or calories. 

73. Factors must be in correct proportion. — If there is 
not enough moisture to furnish sufficient soluble plant-food, 
part of the solar energy is wasted, while on the other hand if 
there is more food brought to the roots than the solar energy 
can utilize, the food material is wasted. In the arid districts 
too little food is available, under natural conditions, for the 
solar energy, but when, through irrigation, a large amount of 
food is made available, large crop yields result. Moisture is 
the controlling factor in these regions. In the highest lati- 
tudes, there is generally an excess of moisture and a deficiency 
of heat. These are the conditions that prevail in much of nor- 
thern Europe, Alaska, and some high mountain regions. 
Here the crop yields are largely a question of temperature 
variations. 

74. Requirements vary. — Different plants require unlike 
proportions of moisture, heat, and sunshine, and most 

23 



24 AGRICULTURAL METEOROLOGY 

plants require varying amounts for best growth at different 
stages of development. A few plants require hot arid climates 
while others reach their best development only in cold moist 
regions. 

75. Critical periods of growth. — Many plants have a 
certain (frequently short) period during growth when there 
must be a well-defined combination of certain weather factors 
to produce large crop yields ; others have the ability to stand 
nearly dormant when unfavorable conditions prevail, but 
will revive and make an excellent growth when the weather 
factors are in correct proportion. 

76. To determine critical period. — There are three well- 
defined methods for determining the most critical period of 
growth of farm crops and the weather factor having the great- 
est influence in varying the yield: (1) Laboratory experi- 
ments; (2) field observations; (3) correlations of weather 
with past records of crop yields. 

77. Laboratory experiments. — One method is to carry 
out laboratory experiments in which the various factors can 
be under control. The moisture, temperature, and sunshine 
are the most important meteorological factors, and by keep- 
ing two of these constant and varying the other, its influence 
can be determined. Or one can be kept constant and the other 
two varied. Some work of this kind has been done, but the 
experiments that may and should be made are sufficient to en- 
gage the attention of many men. It requires special apparatus 
and close attention and should be attempted only by trained 
plant physiologists, or ecologists. 

78. Field observations. — With the most carefully ar- 
ranged details, the conditions that surround plants in the 
field can hardly be duplicated in the laboratory tests. Hence 
it is desirable that detailed records be made of all the 
meteorological factors and the growth and yield of various 
crops at many different places and covering a period of 
many years. 

79. Observations in Russia. — Russia was the pioneer in 
the organization of a group of agricultural-meteorological and 
horticultural-meteorological stations to determine quantita- 
tively the relation of different climatic factors to crop produc- 
tion. The Russian Bureau of Agricultural Meteorology was 
authorized in 1894 and observations were begun in 1896. In 



AGRICULTURAL METEOROLOGY 25 

1912 Russia had observations under way at eighty-one differ- 
ent experiment stations where meteorological records were 
being kept as near as possible to the test plats. 

80. Records in Canada. — Similar records were begun in 
Canada in 1915 at fourteen different experiment farms where 
particular attention was given to spring wheat. Some results 
have been published, but the records should cover several 
years to -make the correlations conclusive. 

81. Records in the United States. — A division of Agri- 
cultural Meteorology was organized in the United States 
Weather Bureau early in 1916, and one of the first important 
things done was to start plans for the inauguration of agri- 
cultural meteorological stations at each of the main agricul- 
tural experiments stations in each state. The war emergency 
made it necessary to hold these plans in abeyance, however. 
It is believed by the chief of this Division that this is one of 
the most important steps that can be taken in the interest of 
agriculture in this or any other country. The climate of the 
United States is so varied, the crops are so diversified and the 
yield so variable, that a careful record of all the weather fac- 
tors and the consequent development of the crop plants must 
be made for several years to determine the critical periods of 
growth. 

82. Value of records. — If it is found, for example, that a 
light rainfall in May means a small hay crop, other forage 
crops can be planted. If it has been learned that the crop 
of winter grains will be reduced by certain weather during the 
winter, the spring grain area can be increased if these weather 
conditions prevail. When the water requirements of various 
crops are determined for different stages of growth, water can 
be more economically handled in the arid and semi-arid re- 
gions of the West. The climate of a district will be more care- 
fully studied and crops planted that are best adapted to the 
prevailing climate, or where the season is long enough, seed- 
ing will be done at such a tiiue as will bring the critical period 
of growth when the weather factor most affecting it will be 
nearest its optimum for that crop. There are innumerable 
ways in which this knowledge can be applied. Much has 
already been done by experiment stations in this direction 
but the work lacks the system and correlation that would be 
obtained under definite direction. 



26 AGRICULTURAL METEOROLOGY 

83. Correlation of weather with past records of crop 
yields. — While records and results are being accumulated 
by laboratory experiments and field observations, much valu- 
able knowledge can be obtained by a mathematical correla- 
tion of accumulated climatic data with records of crop yields 
during past years. The manner of making these correlations 
will be explained in Chapter IV and some of the results al- 
ready obtained will be shown in Chapters VII to IX. 

84. Not a new science. — While the term "agricultural 
meteorology" is new, the importance of studying the relation 
of weather to crops has been recognized and referred to by 
agriculturists and meteorologists for many years. Measure- 
ments of rainfall were made in Palestine in the first century 
of the Christian era, and there was a network of rainfall sta- 
tions in the important rice-growing districts of Korea as early 
as the middle of the fifteenth century. As this crop needs a 
large amount of moisture during its growth, it is only reason- 
able to suppose that the farmers of Korea made a practical 
use of their knowledge of the distribution of moisture in con- 
nection with the growth of this important food crop. 

LABORATORY EXERCISES 

1. Paragraph 77. Carry out some laboratory experiments as in- 
dicated in paragraph 77. Consult the plant physiologist, 

2. Paragraph 78. All students should keep a detailed record of 
weather effects. In the summer select some particular plant or field, or 
some fruit-tree, and record its growth and condition in connection with 
the weather condition prevailing. Determine the moisture-content of 
the soil at frequent intervals (consult the agronomist) ; record the tem- 
perature of the soil each day. 

In winter keep a record of the snowfall and the depth of snow cover- 
ing and its effect on grain and grass fields. 

Record the effect of temperature and sunshine on fruit-buds ; note 
any swelUng and subsequent temperature damage. 

Record the effect of variations in sunshine on greenhouse plants. It 
has been found that head lettuce that is raised in such large quantities 
in greenhouses about Boston cannot be successfully grown in the vicinity 
of Cleveland, Ohio. Why? Is it because of less winter sunshine at the 
latter place ? 

Record the effect of temperature on the amount of food consumed by 
stock. 



AGRICULTURAL METEOROLOGY 27 



REFERENCES 

Agricultural Meteorology. R. F. Stupart. Agricultural Gazette, No. 
3, 1914. 

Agricultural Meteorology. J. Warren Smith. Presidential Address, 
Proceedings of the Ohio Academy of Science. Vol. VI, Part 5, 
1915. pp. 241-261. 

Agricultural Meteorology. J. Warren Smith. Section II, Proceedings 
of the 2d Pan American Scientific Congress, 1916. pp. 75-90. 

Crops and the Weather. P. Broounoff. Bulletin of the Foreign Agri- 
cultural Intelligence, May, 1916. pp. 373-402. 

Economic Cycles: Their Law and Cause. II. L. Moore. The Mac- 
millan Company, 1914. 

Experiment Station Record (editorial). May, 1916. 

Importance of Agricultural Meteorology from the International point 
of view. Girolamo Azzi. Bulletin of the Foreign Agricultural In- 
telligence, February, 1916. pp. 138-143. 

Meteorology in Canada in Relation to Agriculture. R. F. Stupart and 
R. W. Mills. Bulletin of the Foreign Agricultural Intelligence, 
April, 1916. p. 307. 

Methods for the Study of Agricultural Meteorology. V. O. Askinazi, 
Bulletin of Agricultural Intelligence and Plant Diseases, No. 9, 
1912. 

Some Facts concerning the Meteorological Bureau of the Scientific Com- 
mittee of the Russian Ministry of Agriculture. P. Broounoff. Bul- 
letin of the Foreign Agricultural Intelligence, February, 1916. 
pp. 143-147. 

Some Considerations of the Organization of the Agricultural Meteor- 
ological Service. P. Broounoff. Bulletin of the Foreign Agricultural 
InteUigence, April, 1916. pp. 309-314. 

Some Relations of Meteorology with Agriculture. Henry MeUish. 
Quarterly Journal of the Royal Meteorological Society, April, 1910. 

What the Weather Bureau is doing in Agricultural Meteorology. P. C. 
Day. Monthly Bulletin of Agricultural Intelligence and Plant Dis- 
eases, May, 1915. 



CHAPTER III 

AGRICULTURAL CLIMATOLOGY 

That branch of agricultural meteorology which deals with 
the relation of climate to vegetation and farm operations is 
called ''agricultural climatology." The climate largely de- 
termines the vegetation natural to a region, the kind of crops 
that can be grown profitably and, therefore, the types of farm- 
ing, and in a general way the characteristics of the people who 
live in any region. 

85. Climate and man. — It has been stated that the native 
of the tropics, where nature is lavish and provides food ready 
for use by simply gathering it, where only slight protection 
is needed from rain and wild beasts, and where custom ex- 
pects the simplest as well as a very slight amount of clothing, 
has, by building a simple hut and planting a few bread-fruit 
trees, made as full a provision for his family as the man in the 
upper temperate region by building a warm house and carrying 
on the cultivation of large crop areas. In each case the neces- 
sities of life are provided. 

86. In the arctic, where agriculture is not possible, the 
food of man is fish and meat. His houses are made of drift- 
wood and ice and snow, while clothing is from skins. His 
wants are few and these regions are inhabited by a happy and 
improvident people. 

87. In the temperate zone. — The most highly developed 
people are in the temperate zone. In the tropics life is too 
easy and in the arctic too hard, and in each case the wants 
are few and there are found the people least developed men- 
tally and physically. In the temperate regions where man 
must work through the growing season to provide food for 
the winter, where there is a constant struggle to keep the 
fields free from weeds and the encroaching native vegetation, 
are the most inventive and best developed people in every 
way. 

28 



AGRICULTURAL CLIMATOLOGY 29 

88. Native vegetation a key to field crops. — A study of 
the native vegetation will frequently enable one to determine 
what crops can be grown most profitably, and it is the prob- 
lem of the plant ecologist to establish these relations. In some 
sections of the Rocky Mountain region, the ''grass-steppe," 
the "sage-brush steppe," the "pinyon pine juniper," the 
"yellow pine," the "lodge-pole pine," and the "Engelmann 
spruce-balsam" represent zones of increasing rainfall but de- 
creasing temperature, respectively, and show well defined 
agricultural possibilities. In the grass-steppe, the tempera- 
ture is high enough for field crops, but the rainfall is insuffi- 
cient. In the Engelmann spruce-balsam fir forest zone, on 
the other hand, the annual rainfall may run as high as on the 
best agricultural lands in the East, but the temperature is too 
low and the growing season too short for crops, although sum- 
mer grazing is excellent in the open parks. Between these 
extremes and corresponding to the respective zones, are: (a) 
excellent farming and orchard lands; (b) small grains, pota- 
toes, garden crops, and orchards; (c) oats, barley, potatoes, 
alfalfa, and hardy garden crops; and (d) grazing only. 

89. Importance of temperature. — While the lack of mois- 
ture is the limiting factor in successful agriculture in many 
sections, the temperature is the most important factor in de- 
fining the large areas of certain crop distribution or plant va- 
rieties. In the north temperate zone it is the winter tem- 
perature that limits the northern distribution of crops, and 
the summer temperature that restricts them at the southern 
edge. 

90. Seasonal development of crops. — The seasonal de- 
velopment of all vegetation is determined by the climate of 
the particular region. Hopkins has determined that, other 
things being equal, the variation in the time of occurrence of a 
given periodical event in life activity under the influence of 
climate, obeys a well defined law. 

91. Bioclimatic law of latitude, longitude, and altitude. — 
Hopkins has given the above designation to the law that 
shows the variation in climate and through that the develop- 
ment of plants and of insect activities. He states that in tem- 
perate North America this variation is at the general aver- 
age rate of four days to each degree of latitude, each 5 degrees 
of longitude, and each 400 feet of altitude. The phenological 



30 AGRICULTURAL METEOROLOGY 

dates are later northward, eastward, and upward in the spring 
and early summer, and the reverse in the late summer and fall. 

92. Local influences. — Departures from this general law 
are the result of local factors. Accelerating influences are 
sunshine, dryness, prevailing warm winds, southern slopes, 
broad valleys, sandy soils, absence of large bodies of water, 
and the like. The retarding influences are the opposite con- 
ditions. Southern or northern slopes may vary this rule from 
one to four days, while coastal influences may amount to ten 
to fourteen days. 

93. Practical application of law. — After determining the 
climate at a few well located places, and the average influence 
of this climate in developing vegetation, the climate and plant 
development at other places where records are not available 
can be determined by the bioclimatic law. The proper date 
for seeding winter wheat in order to escape hessian fly dam- 
age, for example, can be determined; the limiting zone of 
natural forest cover can be ascertained; the optimum local- 
ity for growing certain crops found in new regions; the proper 
dates for planting crops with the average time from seeding 
to harvesting, together with the possible number of days be- 
tween frosts; the probable date of harvesting crops; the 
probable time of occurrence of insect pests; the proper time 
for spraying found; the northern and southern limit for cer- 
tain crops established, and in general as an aid in solving 
some of the problems constantly coming before the farmer 
everywhere. 

94. An aid in farm management. — In old settled regions, 
the best crops to grow as well as the best methods of han- 
dling the crops have become weU established by the "survival 
of the fittest. " In newer districts, the bioclimatic law, using 
the settled regions as a base, will aid in all kinds of farm oper- 
ations, and in determining the best crops to plant. 

95. Natural vegetation an aid in determining best dates 
for farm operations. — Properly recorded and correctly in- 
terpreted periodical events in natural vegetation serve as ex- 
cellent keys for proper farm operations because these events 
are the result of all the climatic and other factors making up 
the environment. Some examples of commonly recognized 
events in the advance of the season are the following: the 
opinion of the Indians that the proper corn planting time is 



AGRICULTURAL CLIMATOLOGY 31 

when the white oak or maple leaves are the size of squirrel 
ears; the saying in the Rocky Mountain region that sheep 
shearing should not be done until the "spring sown grain be- 
gins to carpet the fields in green, " or *Hhe wool goes off as the 
fruit blossoms come on"; calling the Amelanchier canaden- 
sis, or ''lance-wood" bush the "shad-bush," because when it 
came into bloom it was recognized along the Atlantic Coast 
that it was time to fish for shad. The ornamental shrubs are 
more or less constant in this response to the advance of the 
season and serve as very good guides. 

96. Phenological records desirable. — Every person inter- 
ested in agriculture should keep detailed records of the sea- 
sonal events of a few native trees, the dates of planting of va- 
rious crops, whether this planting was at the proper season to 
produce quick germination, rapid growth, and seasonal ma- 
turing, and above all a record of the prevailing weather and 
its effects. 

97. Records from simple meteorological instruments val- 
uable. — A properly located rain-gage, and a set of maxi- 
mum and minimum thermometers exposed in an inexpensive 
shelter, will give records of very great value in handling farm 
work and in studying the effect of the weather on the condi- 
tion of different soils and the growth and yield of various 
crops. The expense is small and the time necessary for the 
records very little, while the results are very illuminating. 
But with or without instruments, a daily journal of the 
weather will be of untold interest and value as one year 
follows another with its problems and queries as to reasons 
for crop failure or success, insect activities, results of spray- 
ing, and the like. 

LABORATORY EXERCISES 

1. Paragraph 88. Make maps of climate and zones of vegetation. 
Different varieties of forests, different field, garden, and fruit crops. 

2. Paragraph 89. Chart seasonal temperatures and crop distribu- 
tion. 

3. Paragraph 91. Verify the bioclimatic law by charting known dis- 
tribution of well defined vegetation. 

REFERENCES 

Botany of Crop Plants, The. W. W. Robbins. Blakiston, 1917. 
Climate and Plant Growth in certain Vegetative Associations. A. W. 
Sampson, U. S. Department of Agriculture Bulletin No. 700. 



32 AGRICULTURAL METEOROLOGY 

Climate of Wisconsin and its Relation to Agriculture, The, A. R, 
Whitson, O. E. Baker, Bulletin 223, July, 1912, Wisconsin Agricul- 
tural Experiment Station. 

Corn Crops in the United States. H. Arctowski, Reprint from Bulletin 
of American Geographical Society, Vol. XLIV, October, 1912. 

Crop Centers of the United States. A. E. Waller, Journal of the Amer- 
ican Society of Agronomy, February, 1918. 

Effect of Climate and Soil upon Agriculture, The. R. R. Spafford. 
Reprint from University Studies. Lincoln, Nebraska, 1916. 

Effect of Weather upon the Yield of Corn, The. J. Warren Smith, 
Reprint from Monthly Weather Review, February, 1914, Vol. 42. 

Effect of Weather upon the Yield of Potatoes, The. J. Warren Smith, 
Reprint from Monthly Weather Review, May, 1915, Vol. 43. 

Geography of the World's Agriculture, Office of Farm Management, 
U. S. Department of Agriculture, 1917. 

Graphic Summary of World Agriculture, A. V. C. Finch, O. E. Baker, 
and R. G. Hainsworth, Department of Agriculture Yearbook 
Separate No. 713, 1916. 

Growth of Maize Seedlings in Relation to Temperature. P. A. Lehen- 
bauer, Physiological Researches No. 5, Vol. I, Dec, 1914, 

Native Vegetation and Climate of ^Colorado in the relation to Agri- 
culture. Colorado Agricultural Experiment Station Bulletin 224. 

Periodical Events and Natural Law as Guides to Agricultural Re- 
search and Practice. C. G. Hopkins. Monthly Weather Review 
Supplement No. 9, 1918. 

Phenological Dates and Meteorological Data Recorded at Wauseon, 
Ohio, by Thomas Mikesell. J. Warren Smith. Monthly Weather 
Review Supplement No. 2, 1915. 

Physiological Temperature Indices for the Study of Plant Growth in 
Relation to Climatic Conditions. B. E. Livingston, Physiological 
Researches No. 8, Vol, I, April, 1916. 

Relation between Climate and Crops. C, Abbe. Weather Bureau 
Bulletin No. 36, 1905. 

Relation between Temperature and Crops, The. D. A, Seeley, Re- 
print, 19th Michigan Academy of Science Report, 1917. 

Relation of Meteorological Study to More Logical Systems of Crop- 
ping and Crop Production. J. F. Voorhees. Reprint, Proceedings 
of Society for Promotion of Agricultural Science, 1912, 

Single Index to Represent Both Moisture and Temperature Condi- 
tions as Related to Plants, A. B. E. Livingston, Physiological Re- 
searches, Vol. I, No. 9, May, 1916. 

Transpiration as a Factor in Crop Production. T. A. Kiesselbach, 
Nebraska Experiment Station Research Bulletin No. 6, 1916. 

Climate and Meteorology of Australia, The. H. A. Hunt, Bulletin 
No. 9, Reprint from Federal Handbook of Australia, June, 1914. 



AGRICULTURAL CLIMATOLOGY 33 

Climatic Areas of the United States. B. E. Livingston, Reprint from 
Proceedings of American Philosophical Society, Vol. LII, No. 209, 
April, 1913. 

Preliminary Study of Climatic Conditions in Maryland, A. As Re- 
lated to Plant Growth, F. T. McLean, Special Publication of Mary- 
land Weather Service, Vol. IV, part la. Also Physiological Re- 
searches No. 2, 1917. 

Quantitative Study of Climatic Factors in Relation to Plant Life, The. 
J. Adams. Transactions Royal Society of Canada, Series III, 
Vol. X, 1916. 

Relation of Climate to Plant Growth in Maryland. F. T. McLean, 
Monthly Weather Review, February, 1915. 

Relations of Climate to Business, The. Issued by the Chamber of 
Commerce of the U. S. of America, December 3, 1915, Special 
Bulletin. 



CHAPTER IV 

CORRELATION 

This chapter will explain briefly some of the simpler meth- 
ods for finding the relation between definite weather con- 
ditions and the yield of crops. The advanced student who 
wishes to take up the matter in a more mathematical way 
should consult text-books on harmonics and the theory of 
statistics, and the references at the end of the chapter. 

98. A common method. — Figs. 11, 41, 42, illustrate the 
common method of showing the relation between two or more 
factors. A horizontal line through the center of the chart is 
considered the normal for all the factors, while figures at the 
side indicate values above or below this normal. The years 
are given at the top of the page. 

Each curve is drawn independently of the others by plac- 
ing a dot under each year opposite the side figures that show 
the value of the particular factor for that year. The dots are 
then connected by proper lines. 

In Fig. 11, the solid line. A, shows the departure of the po- 
tato yield from the normal from year to year in Ohio. The 
broken line, B, indicates the departure of the total average 
rainfall of Ohio for June and July of each year from the nor- 
mal. The dotted line, C, shows the departure of the average 
temperature from the normal for the same months. 

99. Relation of lines. — It is customary to say that when 
two curves run together, that is, when one runs above the 
normal line and the other does the same, and when one goes 
below the normal line, the other usually follows, or when they 
run in opposite directions, they show a correlation between 
the factors, positive in the first case and negative in the sec- 
ond. On this chart, therefore, inasmuch as the lines A and B, 
representing respectively potato yield and rainfall, appear to 
follow each other in a general way, it may be assumed that 
there is some relation between the rainfall of June and July 

34 



CORRELATION 



35 



and the yield of potatoes. On the other hand, a careful in- 
spection of curves A and C indicates an opposite bending of 
the lines, and hence there must be a negative correlation. 
The difficulty with this method of correlation, however, is 
that while with two curves only a very general comparison 



1884 
1885 
1886 
1887 
1888 
1889 
1890 
1891 
1892 
1893 
1894 
1895 
1896 
1897 
1898 
1899 
1900 
1901 
1902 
1903 
1904 
1905 
^906 
1907 
1908 
1909 


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A/ORMAL B 
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Fig. 11. 



-Relation of weather to the yield of potatoes in Ohio, 
1883-1909. 



can be made, with three or more curves there seems to be 
only a confusion of lines. 

While this method can be used to show roughly the rela- 
tion between two factors, it is not recommended for careful 
work, and not at all when three factors are involved, because 
of the confusion of lines. 

100. A better method. — If three curves are to be used, 
it is far better to arrange the years so that one of the factors 
will have an increasing or decreasing value, as in Fig. 12. In 
this chart the years are arranged so that the curve showing 
the yield of potatoes runs from the highest yield regularly to 
the lowest. Then, by drawing the other curves for the years 



36 



AGRICULTURAL METEOROLOGY 



as shown at the top, broad general correlations can be shown. 
It will be found better in practice, however, to put only two 
curves on the same diagram. 

Examination of the curves on this chart indicates a slight 
general relation between the yield and rainfall, and a strong 
opposite relation between the yield and temperature. When 



1906 
1883 
1891 
1904. 
1909 
1902 
1896 
1903 
1888 
1886 
1905 
1908 
1900 
1907 
1884 
1885 
1889 
1899 
1894 
1895 
1898 
1892 
1893 
1901 
1890, 
1897 
1887 


1 1 Q 

1 K^ 

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44.0 +400+40 
+ 35 +3.50 +J5k 
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A/OPMAL 

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' Fig. 12. — Relation of rainfall and temperature to the yield of potatoes 
in Ohio, 1883-1909. 

the yield is above the normal, the temperature is nearly al- 
ways below normal, and when the yield is low the tempera- 
ture is generally high. 

101. Proper way to find the relation between two vari- 
ables. — In all attempts to ascertain the relation between 
two variables, such as rainfall or temperature and crop yield, 
three steps are necessary: (1) Plot the data as in Figs. 13 to 
17; (2) proceed to find the equation of the data on the chart 
by the method of least squares and trace the calculated 
straight line or curve of nearest fit; (3) if it is found that the 
relation between the two variables can be represented by a 



CORRELATION 



37 



straight line quite as well as by a curve, the correlation coeffi- 
cient may be calculated. In this case it is not necessary to 
make the calculation under No. 2. 

102. The dot chart the first step. — In all attempts to 
ascertain the relation between two variables, it is practically 
indispensable to make the easily-constructed dot chart, as 
shown in Figs. 13-17. The data for Fig. 13 were taken from 
Table 1 showing the average July rainfall and average corn 
yield in Ohio from 1854 to 1913. 

Table 1. — Average July Rainfall and the Yield of Corn in 
Ohio, 1854 to 1913 





Rainfall, 


Yield, 




Rainfall, 


Yield, 


Year 


inches 


bushels 


Year 


inches 


bushels 


1854 


2.6 


26.0 


1884 


3.8 


33.3 


1855 


5.8 


39.7 


1885 


3.2 


36.8 


1856 


2.6 


27.7 


1886 


2.9 


33.5 


1857 


4.9 


36.6 


1887 


2.2 


30.5 


1858 


4.7 


27.7 


1888 


4.4 


38.9 


1859 


1.6 


29.5 


1889 


4.2 


32.3 


1860 


5.8 


38.2 


1890 


2.0 


24.6 


1861 


3.3 


33.5 


1891 


3.8 


35.6 


1862 


3.6 


30.0 


1892 


3.8 


33.3 


1863 


2.6 


27.0 


1893 


2.5 


29.1 


1864 


2.1 


27.0 


1894 


1.6 


32.6 


1865 


5.7 


35.0 


1895 


2.0 


33.7 


1868 


5.1 


36.5 


1896 


8.1 


41.7 


1867 


3.2 


29.8 


1897 


4.6 


34.3 


1868 


2.7 


34.4 


1898 


4.0 


37.4 


1869 


4.8 


28.4 


1899 


4.2 


38.1 


1870 


4.7 


37.5 


1900 


4.6 


42.6 


1871 


3.7 


36.7 


1901 


2.7 


30.0 


1872 


6.7 


40.9 


1902 


4.7 


38.8 


1873 


6.2 


35.1 


1903 


3.7 


31.5 


1874 


3.8 


39.2 


1904 


4.1 


32.8 


1875 


6.9 


34.2 


1905 


3.9 


37.9 


1876 


6.4 


36.9 


1906 


5.1 


42.2 


1877 


3.7 


32.5 


1907 


5.4 


34.8 


1878 


5.4 


37.8 


1908 


4.1 


36.1 


1879 


4.2 


34.3 


1909 


3.8 


38.7 


1880 


4.2 


38.9 


1910 


3.2 


36.6 


1881 


3.6 


31.0 


1911 


2.4 


38.6 


1882 


3.2 


34.0 


1912 


5.7 


42.8 


1883 


4.2 


24.2 


1913 


5.2 


37.8 



38 



AGRICULTURAL METEOROLOGY 











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20 25 JO 35 40 45 50 

y/£LD or CORA/ /A/ BU5HEL5 PER ACRE 

Fig. 13. — Dot chart showing the relation between the July rainfall 
and the yield of corn, Ohio, 1854-1913. 

103. How dot chart is made. — A dot is placed on the 
chart for each year so that its location agrees with the rain- 
fall value and the yield figures for that year. For example, 
on Fig. 13, in 1913, the rainfall averaged 5.2 inches, while the 
yield of corn was 37.8 bushels to the acre, hence the dot (in- 
closed in brackets) was located to agree with these values. 



CORRELATION 



39 



79 
78 
77 










• 


















• 












• 






















• 












76 




























< 










K 


• 






• 


• 










^75 










• 




• 
























74 

K 

|- 








• 
• 


« 


• 


• 






A/OffMAL 










• 


• • 












•- 




,% 


• 


• 








* 






• 


• 


• 










• 
• 






• 




7/ 








• 




















• 






•• 




70 
69 














• 
































i 


























AT 



30 40 60 60 70 80 90 /OO W 

Y/£-LD or POTATOES /Af BU5M£LJ P€ff ACRE 



Fig. 14. — Dot chart showing the relation between the mean tempera- 
ture in July and the yield of potatoes, Ohio, 1860-1914. 



40 



AGRICULTURAL METEOROLOGY 



104. Potato yield and temperature. — Figs. 14 and 15 
were prepared in a similar manner from data giving the mean 
temperature for July and the yield of potatoes in Ohio and 
Portage County, respectively.' 

105. No relation shown in Fig. 15. — When the dots are 
promiscuously scattered over the chart, as in Fig. 15, there is 
no relation between the factors and no further time need be 
spent on their consideration. In other words, Fig. 15 shows 
that the mean temperature for July has no dominating effect 



















• 






o • 




• 












•• 


•• 


• 


o 






• 












• ••• 


• 
























AT 



SO 60 70 80 90 lOO /lO /20 IJO 

Y/ELO or PoraTOEs in bushels per acre 

Fig. 15. — Dot chart showing the relation between the mean tempera- 
ture in July and the yield of potatoes in Portage County, Ohio, 1884- 
1913. 



on the yield of potatoes in Portage County, Ohio. (See Chap- 
ters VII, VIII, and IX for further discussion of this matter.) 

106. A negative relation in Fig. 14. — Fig. 14, however, 
shows clearly that in general a warm July is unfavorable for 
potatoes in the state of Ohio as a whole, and that a cool July 
is usually followed by a yield of potatoes above the normal. 
The lines in the center of the chart indicate normal tempera- 
ture and yield values. 

107. Fig. 13 indicates a positive relation. — When the dots 
are grouped as in Fig. 13, a positive relation is indicated. In 
this particular case, the chart shows that the heavier the rain- 



CORRELATION 41 

fall in July in Ohio, the greater the corn yield will be, in gen- 
eral. Both figures will be discussed further in Chapter VIII. 

108. When mathematical correlations should be made. — 
The dots in Figs. 13, 14 and 15 indicate not only that there 
is a relation between the two factors, but that this relation 
can be represented by a straight line. When the dots show a 
definite linear relation or a relation that can be represented 
by a curve, then the best fitting line or curve should be deter- 
mined. This is step No. 2, under paragraph 101, and gives 
the definite relation between the two variables. The for- 
mula can be used in calculating one from the other, such as 
yield from rainfall. 

109. To determine the straight line of nearest fit. — The 
calculation of the straight line of nearest fit by the method 
of least squares will be illustrated by a method recently 
evolved by the author for predicting minimum temperatures 
on nights when radiation conditions prevail. The dot chart 
in Fig. 16 shows for San Diego, California, the relation be- 
tween the depression of the dew-point temperature from the 
air temperature in the late afternoon, and the variation of the 
minimum temperature during the following night from the 
evening dew-point, as indicated by the figures and legend on 
the chart. The line A, B, was calculated by the method of 
least squares, as shown by the following. 

110. Equation for a straight line. — The equation for de- 
termining the straight line of nearest fit, such as A, B, in 
Fig. 16, is y = a+bR. In this^case R is the depression of 
the evening dew-point {i. e., the number of degrees that the 
dew-point is below the dry bulb or current temperature at the 
evening observation); y is the variation of the minimum 
temperature during the coming night from the evening dew- 
point, or the value that is desired in predicting the minimum 
temperature. The values a and b are unknown factors that 
are determined by Table 2 and the calculation following. 



42 



AGRICULTURAL METEOROLOGY 





























































































































y' 




























/ 


/ 




























/ 


/ 
























































• 


/.: 




























"'/ 


/' 




























y< 


/ 




























y 




* 




















• * 


; 


' y 


;-•■: 


' 






/? = 


y=VA/ 
TEMP 


y = a + t>H = LINL Ati 
CSS'OA/ or THE DCW POff 
9/AT/ON or THC MINIMUM 


\IT 






'J- 


A' 












ERATURC F/^ 
POIN 


10M 

T 


rne L 


■IEV</ 






^ 


















1 


laoj 








-4 


ky 


• 


























































AT 



O 5 lO 15 20 eS 30 J5 40 45 50 55 60 &5 70 . 75 60 

DSPRESSlON or THC EVeNING DCW POINT DCG. F 

Fig. 16. — Dot chart showing the relation between the variation of the 
dew-point from the current temperature (the depression of the dew- 
point) at the evening observation, and the variation of the minimum 
temperature from the evening dew-point. San Diego, California, 
radiation nights in November from 1897-1916. 



CORRELATION 43 



Table 2. — Relation Between the Depression of the Dew-point 
IN the late Afternoon, and the Variation of the Minimum 
Temperature During the Night from the Evening Dew- 
point. San Diego, Cal., 20 Novembers to 1916 

(2) 



(1) 








R 


y 


i22 


Ry 


79 


+64 


6241 


+5056 


63 


+44 


3969 


+2772 


44 


+29 


1936 


+ 1276 


53 


+33 


2809 


+ 1749 


57 


+32 


3249 


+ 1824 


56 


+30 


3136 


+ 1680 


51 


+35 


2601 


+ 1785 


49 


+27 


2401 


+ 1323 


39 


+ 14 


1521 


+ 546 


46 


+27 


2116 


+ 1242 


36 


+ 10 


1296 


+ 360 


27 


+ 14 


729 


+ 378 


44 


+27 


1936 


+ 1188 


36 


+21 


1296 


+ 756 


27 


+ 14 


729 


+ 378 


35 


+21 


1225 


+ 735 


33 


+18 


1089 


+ 594 


24 


+ 9 


576 


+ 216 


47 


+25 


2209 


+ 1175 


36 


+21 


1296 


+ 756 


33 


+20 


1089 


+ 660 


34 


+20 


1156 


+ 680 


24 


+ 11 


576 


+ 264 


21 


+ 7 


441 


+ 147 


43 


+24 


1849 


+1032 


37 


+21 


1369 


+ vvv 


29 


+16 


841 


+ 464 


28 


+ 13 


784 


+ 364 


26 


+ 9 


676 


+ 234 


24 


+ 7 


576 


+ 168 


16 


+ 2 


256 


+ 32 



R 


y 


ij;2 


Ry 


23 


+ 9 


529 


+ 207 


17 


+ 5 


289 


+ 85 


36 


+30 


1296 


+ 1080 


25 


+ 16 


625 


+ 400 


16 


+ 6 


256 


+ 96 


13 


— 1 


169 


— 13 


8 


+ 8 


64 


+ 64 


23 


+ 9 


529 


+ 207 


22 


+ 8 


484 


+ 176 


14 


+ 5 


196 


+ 70 


28 


+13 


784 


+ 364 


16 


+ 1 


256 


+ 16 


14 





196 





8 


— 2 


64 


— 16 


38 


+23 


1444 


+ 874 


27 


+ 13 


729 


+ 351 


22 


+ 8 


484 


+ 176 


14 


+ 8 


196 


+ 112 


11 


+ 3 


121 


+ 33 


37 


+ 16 


1369 


+ 592 


34 


+16 


1156 


+ 544 


24 


+10 


576 


+ 240 


14 


+ 3 


196 


+ 42 


11 


— 1 


121 


— 11 


31 


+ 15 


961 


+ 465 


29 


+10 


841 


+ 290 


29 


+ 1 


841 


+ 29 


20 


+ 8 


400 


+ 160 


20 





400 





13 


+ 1 


169 


+ 13 


26 


+ 8 


676 


+ 208 



44 AGRICULTURAL METEOROLOGY 



(3) San Diego, Cal., 


, continued. 


(4) 








R 


y 


R^ 


Ry 


R 


y 


i22 


Ry 


24 


+ 9 


576 


+216 


7 


— 3 


49 


—21 


20 


+ 6 


400 


+ 120 


7 


— 6 


49 


—42 


11 


— 4 


121 


— 44 


7 


— 4 


49 


—28 


21 


+ 9 


441 


+ 189 


5 


— 9 


25 


—45 


20 


+ 7 


400 


+ 140 


1 


— 6 


1 


— 6 


17 


+ 5 


289 


+ 85 


18 


+ 4 


324 


+72 


11 





121 





16 


+ 2 


256 


+32 


17 


+ 8 


289 


+136 


14 


+ 1 


196 


+14 


13 


— 6 


169 


— 78 


10 


+ 1 


100 


+ 10 


12 


+ 1 


144 


+ 12 


8 


— 4 


64 


—32 


21 


+ 7 


441 


+147 


8 


— 5 


64 


—40 


14 


— 1 


196 


— 14 


7 


— 6 


49 


—42 


14 


+ 6 


196 


+ 84 


5 


— 4 


25 


—20 


11 





121 





4 


— 9 


16 


—36 


10 


— 2 


100 


-- 20 


4 


— 9 


16 


—36 


23 


+ 10 


529 


+230 


17 


+ 4 


289 


+68 


18 


+ 6 


324 


+ 108 


12 


— 3 


144 


—36 


14 


+ 2 


196 


+ 28 


9 


— 1 


81 


— 9 


13 





169 





8 





64 





11 


+ 8 


121 


+ 88 


7 


— 4 


49 


—28 


9 


- 2 


81 


— 18 


5 


— 3 


25 


—15 


9 


+ 1 


81 


+ 9 


19 


— 4 


361 


—76 


7 


— 6 


49 


— 42 


10 


— 5 


100 


—50 


19 


+ 10 


361 


+ 190 


8 


+ 1 


64 


+ 8 


13 


— 1 


169 


— 13 


7 


— 2 


49 


—14 


7 


+ 7 


49 


+ 49 


4 


—10 


16 


—10 


5 





25 





3 


— 9 


9 


—27 


5 


— 4 


25 


— 20 


2 


—11 


4 


—22 


4 


— 9 


16 


— 36 


15 


+ 3 


225 


+45 


17 


+ 3 


289 


+ 51 


11 


— 4 


121 


—44 


17 


+ 7 


289 


+ 119 


8 


— 9 


64 


—72 


10 


— 3 


100 


— 30 


7 


— 3 


49 


—21 


7 


— 5 


49 


— 35 


7 


— 1 


49 


— 7 


6 


— 6 


36 


— 36 


6 


— 6 


36 


—36 


17 


+ 2 


289 


+ 34 


6 


— 8 


36 


—48 


11 


— 2 


121 


— 22 


6 


— 4 


36 


—24 


7 


— 5 


49 


— 35 


5 


— 3 


25 


—15 


7 


— 1 


49 


— 7 


5 


— 5 


25 


—25 


7 





49 





13 





169 








CORRELATION 




EGO, CaL.j 


, continued. 






R 


y 


i22 


Ry 


12 


+1 


144 


+12 


8 


2 


64 


-16 


10 


-8 


100 


-80 


8 


-5 


64 


-40 


6 


-6 


36 


-36 


4 


-6 


16 


-24 


5 


-6 


25 


-30 


4 


-8 


16 


-32 


4 


-4 


16 


-16 


9 


— 1 


81 


- 9 


6 


-2 


36 


-12 


6 


-4 


36 


-24 


3 


-9 


9 


—27 


6 


-7 


36 


-42 


4 


-9 


16 


-36 


5 


— 2 


25 


-10 


6 


+ 1 


25 


+ 5 


4 


— 7 


16 


-28 


3 


-9 


9 


—27 


4 


-5 


16 


-20 


3 


—7 


9 


-21 


4 





16 






45 



Sums 2803 = :SR + 720 = % 80,093 = 2R2 + 37,829 = ^Ry. 
(162 items = n) 

R = Depression of the dew-point. 
y = Variation of the minimum from the evening dew-point. 

111. To determine values of a and b. — The values of 
the unknown quantities a and b in the equation y = a + bR, 
are determined by the following equation and calculation : 

... . _ n(2:Ry)-(i:R)(Zy) 
^ ^ n(2:R2) — (SR)- 

Inserting the values at the foot of the table we have, 

(9^ h - 162(37829) -(2803) (720) _ 

^^^ ^ ~ 162(80093) - (2803)2 " ^"^^'^ 

(3^^^Zy-b(ZR) 



46 AGRICULTURAL METEOROLOGY 

Inserting the values in the table, and the value of b, 
we get, 

^ ^ 162 

112. To locate line AB. — After finding the values of a 
and b, it becomes a simple matter to insert them in the equa- 
tion y = a + bR, and compute y. For example, if the dew- 
point at the evening observation is 30° below the current 
temperature, the equation becomes 

y = -9.5 + 0.803 X 30 = 14.6 
A mark is then placed on the 30 perpendicular line oppo- 
site the value of 14.6 at the left. One other point is located 
in the same manner and the straight line AB is drawn. This 
is the method which should be followed on all dot charts 
where an inspection shows that the relation is linear. 

113. When a curve fits the data best.— After the dot 
chart has been made, if an inspection shows that a curve will 
fit the data better than a straight line, as in Fig. 17, the problem 
is to find some form of curve that will represent the arrange- 
ment of dots with satisfactory accuracy. If the curvature is 
not great and there are points of inflection, the parabola or 
possibly the hyperbola may be the simplest forms to try. In 
this case the deviation from a straight line is not great and is 
fairly regular, hence it seems probable that the data may be 
represented by some portion of some parabola which is per- 
haps the simplest type of curve likely to be suitable. 

114. Evaluation of the coefficients. — Having chosen the 
type of curve, the next problem is to evalulate the unknown 
coefficients. It is a well known principle in algebra that the 
values of unknown terms in equations can be calculated only 
when there are just as many independent simultaneous equa- 
tions between the quantities as there are unknown terms to 
be found. 

115. Least square method. — The least square method is 
simply a mathematical scheme by which a large nuniber of 
observations may be combined in a manner which will give 
the required or so-called ''normal" equations and at the 
same time according to a principle which will give the best 
fit. Whether the type chosen be a straight line, parabola, or 
other curve, the least square solution gives at once the partic- 



CORRELATION 47 

ular line of that type which fits best, but whether some other 
type of line will fit still better can be found only by trial, that 
curve being the best for which the standard deviation is a 
minimum. 

116. The equation for a parabola. — The equation of a 
parabola may be written y = a + bx + cx^, in which the 
coefficients a, b, and c are commonly designated as constants 
whose values are either known beforehand or must be deter- 
mined in order that the curve may fit some particular case. 
The quantities x and y may have almost any value in pairs 
and are called variables. For some arrangements of data the 
equation might need to be written 

X = a + by + cy2 

but the same result would be gained simply by transposing 
the scheme of plotting the data. Inasmuch as the last let- 
ters of the alphabet are commonly used to designate unknown 
quantities, the first equation is changed to read 

V = X + by + cz 

in which x, y, and z are the coefficients to be determined; b 
is the evening relative humidity; c the square of the relative 
humidity and v the variation of the minimum temperature of 
the following morning from the evening dew-point, or the 
value desired in making a forecast of the minimum tempera- 
ture on radiation nights. 

117. Star point method for calculating the parabolic 
curve. — The use of the least square method is generally 
tedious and laborious, especially when large quantities of 
data must be treated and when three or more unknowns are 
to be found, although it must be employed in many cases. 
On the other hand, the present and many other similar prob- 
lems may be solved much more expeditiously and without 
sacrifice of useful accuracy by what Charles F. Marvin, Chief 
of the Weather Bureau, has called the '^star point method" 
in order clearly to differentiate it from the least square 
method. 

118. Star point method applied to other problems. — It 
may be applied to the solution of any problem and supplies 
the required number of ''star" equations simply by the judi- 
cious selection, on the graph, of the required number of 
''star" points, one for each unknown to be evalulated. (See 



48 



AGRICULTURAL METEOROLOGY 



*60 


A 

\. 


















1 


\ 


















•N 


• 






6 

5 
li 

4t 


*■ < 

4B S 
S7 2i 
y 9 160 
V'jr i- by -t-Cz 
JT' 6/5 
y 2 69 
Z = 0. 0394 


5 

5 




1 
















1 

I 




\ 


\ 
















m 




















• 


2 


• 










1 -f-^O 
+5 






• 
• 


• \ 


• 
• 
• 
• 
















• 


\ 


















\ 








^JB — 
















• 





















10 15 

€VCNING 



20 25 30 

aCLATIVt HUMIDITY 



Fig. 17. — Dot chart showing the relation between the evening relative 
humidity and the variation of the minimum temperature from the 
evening dew-point, El Paso, Texas, radiation nights in 1918. 



1, 2, and 3, Fig. 17.) This method simply substitutes in- 
telligent selection of the star points for the tedious least 
square process of forming normal equations, with the further 
convenience that in general the numerical factors are small 



CORRELATION 



49 



numbers, thereby simplifying the solution of the equa- 
tions. 

119. Accuracy necessary.— It seems proper to add a word 
of advice to beginners in regard to securing accuracy in arith- 
metical computations. In problems of the kind under con- 
sideration, it is generally necessary to carry four, or possibly 
five, significant figures throughout the original computations, 
inasmuch as this makes the derived results sufficient!}^ accu- 
rate to show serious disagreement if errors of arithmetic are 
made in the process. At the end of the operation, unneces- 
sary significant figures may be dropped by the usual rules. 
The effect of this may, however, appear by seeming to shift 
the calculated curve so as not to pass exactly through the 
original star points, as should otherwise be the case. 

120. Calculating the parabolic curve. — The process for 
calculating the parabolic curve by the star point method is 
given somewhat in detail for the benefit of the student who 
may not have access to the more complete text-books. After 
the selection of the relative humidity values to be used in 
these equations, the exact locations of the points, 1, 2, and 3 
can be determined by inspection or by calculation from the 
position of the surrounding dots. On this figure, point 1 was 
placed at a relative humidity of 5 per cent with the variation 
of the minimum temperature from the dew-point 48°. At the 
star point 2, the relative humidity is 15 per cent and the varia- 
tion 27°; at point 3 the relative humidity was 40 per cent and 
the variation 9°. 

121. Normal equations. — With these data, the normal 
equations are written as follows: 

Normal Equations 



h 


V 


c 


5 
15 

40 


48 

27 
9 


25 

225 

1600 



In these b is the relative humidity; c the square of the rel- 
ative humidity, and v the variation of the minirimm temper- 
ature from the dew-point. 



50 AGRICULTURAL METEOROLOGY 

From this table the three equations for solving the un- 
known factors X, y, and z are written 

(1) X + biy + ciz = Vi 

(2) X + bsy + C2Z = V2 

(3) X + bsy + C3Z = V3 

The coefficients bi, b2, and bs represent the three values of 
b in this table, viz: 5, 15, and 40; the values of Ci and Vi and 
so on, are the corresponding values of these factors. 

122. Solving for unknown quantities. — The values of x, 
y, and z will be determined by the usual algebraic methods of 
solving for unknown quantities. This may be done by indi- 
cating the work algebraically and solving for each value, or 
preferably by what may be termed the direct solution method. 

123. Solving by direct solution. — Usually the value of z 
can be determined by substituting the known values of b, v, 
and c in the normal equations and then solving. In this case 
equations (1), (2), and (3) become 

(1) x + 5y + 25z = 48 

(2) X + 15y + 225z = 27 

(3) X + 40y + 1600z = 9 
Subtracting equation (2) from equation (1), we get 

(4) _ lOy - 200z = 21. 
Subtracting (3) from (2), we have 

(5) - 25y - 1375z = 18. 

Obtain like coefficients for y by multiplying equation (4) by 
5 and equation (5) by 2 when we get, respectively, 

(6) — 50y- lOOOz = 105, and 

(7) -50y-2750z = 36. 
Subtracting equation (7) from equation (6), we have, 

(8) 1750z = 69, or 

z = 0.03943. 

124. To determine the value of y and x. — The next step 
will be to substitute the value of z in equation (4) or (5) , and 
solve for y. The work will be checked by solving for y in 
both equations and this should be done. Substituting the 
value of z in equation (4) we get 

(9) - lOy - (200 X 0.03943) = 21 

y = - 2.8886. 



CORRELATION 51 

Substituting z in equation (5), it becomes 

(10) - 25y - (1375 X 0.03943) = 18 
y = -2.88865. 
These values of y must agree closely if the arithmetic is cor- 
rect. Substituting the values of y and z in equations (1), (2), 
and (3) we get the following 

(11) X + (5 X -2.8886) + (25 X 0.03943) = 48 

(12) X + (15 X —2.8886) + (225 X 0.03943) = 27 

(13) X + (40 X -2.8886) + (1600 X 0.03943) = 9 
Carrying out the calculation we have for each equation, re- 
spectively, 

X = 61.45725 
X = 61.45725 

X = 61.456, or an average of 
61.457 for the value of x. 

125. Checking the work. — In general, it would be best 
to check the accuracy of ail the arithmetic in the computa- 
tion of coefficients. This is done by substituting the values 
of X, y, and z in equations (1), (2) and (3) which should give 
exactly the absolute terms, in this case 48, 27, and 9. Very 
slight errors will result from dropping digits in the values of 
x, y, and z but appreciable discrepancies indicate arithmet- 
ical errors. 

126. The hygrometric equation for EI Paso, Texas. — By 
using these values: x = 61.46; y = —2.889; and z = 
0.0394 for the unknown quantities in the equation, v = x 
+ by + cz, the probable variation of the minimum tempera- 
ture from the evening dew-point (v) can be determined on 
radiation nights with a fair degree of accuracy at El Paso. 
The parabolic curve will be placed on diagram 17 by utiliz- 
ing the points already selected and calculating others by this 
equation. For a relative humidity of 10 per cent, for example, 
by inserting the known values of b and c, and the above de- 
termined values for x, y, and z, in the equation 

V = X + by + cz, 
it becomes 
(14) V = 61.46 + (10 X -2.89) + (100 X 0.0394). 
Carrying out the calculation, we get, 
V =36.5°. 



52 AGRICULTURAL METEOROLOGY 

By the same method the value of v for other relative humid- 
ity figures is calculated, and then the line AB drawn. 

If the line, as calculated, runs too high or too low, it will be 
evident that the points for making the three normal equa- 
tions were not correctly located, when new points must be 
taken and the work repeated. 

If trials fail to give a satisfactory parabolic curve, it will 
be evident that the line of satisfactory fit is not a parabola, 
but some other curve. Just as the trial of a parabolic curve 
to fit the data shows a closer agreement than a straight line 
gives, so the trial of some other curve than the parabola 
might show by the magnitude of the sum of the squares of 
the residuals which of the two or many curves tried will give 
the best fit, that best fit being shown by the minimum sum 
of the squares. 

127. Practical application of the formula. — Having satis- 
fied oneself that a particular formula is a dependable aid in 
the work in hand, the use of the equation in practical work 
is effected most expeditiously by computing a table or pre- 
paring charts giving the necessary values either of v for a se- 
ries of values b, or providing a larger table or chart giving di- 
rectly the values of v based on the known relations between 
b and v. 

In the following tabulation the variation of the minimum 
temperature from the evening dew-point (v) for certain rela- 
tive humidities (b) at the evening observation at El Paso, 
Texas, are tabulated. This is from the equation v = x + 
by -(- cz when the values of the unknowns, determined from 
the above calculations are, 

X = 61.457; y = 2.889; z = 0.03943. 



6 


c 


hy 


cz 


V 


5 


. 25 


— 14.445 


0.986 


48.00 


6 


36 


— 17.334 


1.3184 


45.44 


7 


49 


— 20.223 


1.9306 


43.16 


8 


64 


— 23.112 


2.5216 


40.87 


9 


81 . 


— 26.001 


3.1914 


38.65 


10 


100 


— 28.89 


3.943 


36.51 


20 


400 


— 57.78 


15.767 


19.44 


30 


900 


— 86.67 


35.487 


10.27 


40 


1600 


—115.56 


63.088 


8.99 


50 


2500 


—144.45 


98.575 


15.58 



CORRELATION 53 

128. Other curves. — If neither the straight hne nor the 
parabohc curve fits the data, other curves may be calculated. 
The hyperbola, for example, involves four unknown quanti- 
ties and requires four normal equations. After these have 
been stated, the solving of the unknown quantities proceeds 
in a similar manner. A text on curve fitting should be con- 
sulted in these operations. 

129. The correlation coefficient. — When the dot chart 
shows a linear relation between the two variables, and it is 
not desired to determine this relation in the definite manner 
that is possible by the calculation indicated in step No. 2, the 
index of the extent to which a relation can be represented by 
a straight line can be determined by finding the correlation 
coefficient, step No. 3. (See paragraph 101). 

130. Definition and explanation. — The correlation coeffi- 
cient may be defined as the mean product of deviations of 
corresponding variates from their mean values in units of the 
standard deviation. 

The correlation coefficient is a measure of the resemblance 
of two sets of observations or the measure of the dependence 
of one phenomenon on another when this dependence is 
linear. 

The theory of the correlation coefficient assumes that a 
series of observations can be represented by a straight line, 
and the correlation coefficient expresses the degree of exact- 
ness, on a basis of to + 1 or to — 1 with which the obser- 
vations fall on that line. The determination of the coeffi- 
cient, further, gives an idea of what the equation of the 
straight line may be. 

131. Most commonly used in showing relation between 
weather and crop yield. — The calculation of the correlation 
coefficient in studying the influence of certain weather fac- 
tors in varying the yield of crops was first applied by G. Udny 
Yule and R. Hooker in Europe, S. M. Jacob of Calcutta, and 
independently in this country by the author. It has since 
come to be the method most commonly used by students of 
weather and crops everywhere. Too much weight should not 
be given to the results of this method, however, unless the dot 
chart shows a well defined linear relation. The dot chart 
should, therefore, always be made before the correlation coef- 
ficient is calculated. 



54 



AGRICULTURAL METEOROLOGY 



132. How to calculate the correlation coefficient. — The 

method of determining the correlation coefficient is illus- 
trated in Table 3, and the discussion following. 



Table 3. Correlation of July Rainfall and the Yield of Corn, 
IN Ohio, 1854 to 1913 



Year 
1 



July rainfall 


Corn yield 


2 3 4 


5 6 7 



Amount Depar- 
ture 



Square 
of depar- 
ture 



Amount 



Depar- 
ture 



8 



Square 

of depar- 3x6 
ture 





Inches 


Inches 




Bushels 


Bushels 






1854 


2.6 


— 1.5 


2.25 


26.0 


-7 


49 


+10.5 


1855 


5.8 


+1.7 


2.89 


39.7 


+7 


49 


+ 11.9 


1856 


2.6 


-1.5 


2.25 


27.7 


-5 


25 


+ 7.5 


1857 


4.9 


+0.8 


.64 


36.6 


+4 


16 


+ 3.2 


1858 


4.7 


+0.6 


.36 


27.7 


-5 


25 


— 3.0 


1859 


1.6 


-2.5 


6.25 


29.5 


-3 


9 


+ 7.5 


1860 


5.8 


+ 1.7 


2.89 


38.2 


+5 


25 


+ 8.5 


1861 


3.3 


-0.8 


.64 


33.5 


+0.4 


. . 


- 0.3 


1862 


3.6 


-0.5 


.25 


30.0 


-3 


9 


+ 1.5 


1863 


2.6 


-1.5 


2.25 


27.0 


-6 


36 


+ 9.0 


1864 


2.1 


-2.0 


4.00 


27.0 


-6 


36 


+12.0 


1865 


5.7 


+ 1.6 


2.56 


35.0 


+2 


4 


+ 3.2 


1866 


5.1 


+ 1.0 


1.00 


36.5 


+4 


16 


+ 4.0 


1867 


3.2 


-0.9 


.81 


29.8 


-3 


9 


+ 2.7 


1868 


2.7 


— 1.4 


1.96 


34.4 


+2 


4 


- 2.8 


1869 


4.8 


+0.7 


.49 


28.4 


-4 


16 


- 2.8 


1870 


4.7 


+0.6 


.36 


37.5 


+5 


25 


+ 3.0 


1871 


3.7 


-0.4 


.16 


36.7 


+4 


16 


- 1.6 


1872 


6.7 


+2.6 


6.76 


40.9 


+8 


64 


+20.8 


1873 


6.2 


+2.1 


4.41 


35.1 


+2 


4 


+ 4.2 


1874 


3.8 


-0.1 


.01 


39.2 


+6 


36 


- 0.6 


1875 


6.9 


+3.0 


9.00 


34.2 


+ 1 


1 


+ 3.0 


1876 


6.4 


+2.5 


6.25 


36.9 


+3 


9 


+ 7.5 


1877 


3.7 


-0.2 


.04 


32.5 


-1 


1 


+ 0.2 


1878 


5.4 


+ 1.5 


2.25 


37.8 


+4 


16 


+ 6.0 


1879 


4.2 


+0.3 


.09 


34.3 


+ 1 


1 


+ 0.3 


1880 


4.2 


+0.3 


.09 


38.9 


+5 


25 


+ 1.5 


1881 


3.6 


— 0.3 


.09 


31.0 


-4 


16 


+ 1.2 


1882 


3.2 


-0.7 


.49 


34.0 


+0.5 




- 0.4 


1883 


4.2 


+0.3 


.09 


24.2 


-9 


81 


- 2.7 



CORRELATION 



55 



Table 3. Correlation of July Rainfall and the Yield of Corn, 
IN Ohio, 1854 to 1913 — Continued 



Year 


July rainfall Com yield 


1 


2 3 4 5 6 7 8 


SqiMre Square 
Amount Depar- of de-par- Amount Depar- of depar- 3x6 
ture ture ture ture 



Inches Inches 



Bushels Bushels 



1884 


3.8 


-0.1 


.01 


33.3 


-0.2 






1885 


3.2 


-0.7 


.49 


36.8 


+3 


9 


-2'l 


1886 


2.9 


-1.0 


1.00 


33.5 


-0.03 






1887 


2.2 


-1.7 


2.89 


30.5 


-3 


9 


+ '5^1 


1888 


4.4 


+0.5 


.25 


38.9 


+5 


25 


+ 2.5 


1889 


4.2 


+0.3 


.09 


32.3 


— 1 


1 


- 0.3 


1890 


2.0 


-1.9 


3.61 


24.6 


-9 


81 


+ 17.1 


1891 


3.8 


-0.1 


.01 


35.6 


+2 


4 


— 0.1 


1892 


3.8 


-0.1 


.01 


33.3 


-0.2 






1893 


2.5 


-1.4 


1.96 


29.1 


-4 


16 


+ 5.6 


1894 


1.6 


-2.6 


6.76 


32.6 


-4 


16 


+ 10.4 


1895 


2.0 


-2.2 


4.84 


33.7 


-3 


9 


+ 6.6 


1896 


8.1 


+3.9 


15.21 


41.7 


+5 


25 


+ 19.5 


1897 


4.6 


+0.4 


.16 


34.3 


-3 


9 


— 1.2 


1898 


4.0 


-0.2 


.04 


37.4 


+0.4 




— 0.1 


1899 


4.2 


+0.01 


.001 


38.1 


+1 


i 




1900 


4.6 


+0.4 


.16 


42.6 


+6 


36 


+ 2.4 


1901 


2.7 


— 1.5 


2.25 


30.0 


-7 


49 


+10.5 


1902 


4.7 


+0.5 


.25 


38.8 


+2 


4 


+ 1.0 


1903 


3.7 


-0.5 


.25 


31.5 


— 6 


36 


+ 3.0 


1904 


4.1 


-0.1 


.01 


32.8 


-4 


16 


+ 0.4 


1905 


3.9 


-0.3 


.09 


37.9 


+ 1 


1 


- 0.3 


1906 


5.1 


+0.9 


.81 


42.2 


+5 


25 


+ 4.5 


1907 


5.4 


+ 1.2 


1.44 


34.8 


-2 


4 


- 2.4 


1908 


4.1 


— 0.1 


.01 


36.1 


-1 


1 


+ 0.1 


1909 


3.8 


-0.4 


.16 


38.7 


+2 


4 


— 0.8 


1910 


3.2 


— 1.0 


1.00 


36.6 


-0.4 




+ 0.4 


1911 


2.4 


-1.8 


3.24 


38.6 


+2 


4 


— 3.6 


1912 


5.7 


+ 1.5 


2.25 


42.8 


+6 


36 


+ 9.0 


1913 


5.2 


+ 1.0 


1.00 


37.8 


+ 1 


1 


+ 1.0 


Sum. 






.111.83 






1,045 


+203.2 



133. Explanation of table. — Eight columns are used in 
the table. Column 1 indicates the items, which in this case 



56 AGRICULTURAL METEOROLOGY 

are the years from 1854 to 1913, inclusive, a period of sixty 
years. 

Column 2 gives the average rainfall for the state of Ohio 
for the month of July for each' of these years. Column 3 
shows the departure of the rainfall for each year, from the 
average or normal for the month. In column 4 these depart- 
ures from the normal have simply been squared. 

In column 5 there has been entered the average yield of 
corn for the state of Ohio for each year, in bushels to the acre. 
Column 6 gives the difference between the yield for each year 
and the normal or average for a long period. 

134. Average corn yield. — The average yield of corn for 
Ohio for the sixty years is 34.5 bushels an acre. A careful in- 
spection of the yield figures, however, will show a gradual in- 
crease in the yield during much of the time, and instead of 
taking the difference between the yield for each year and the 
average for the whole period, it seemed best to use the mean 
for each twenty years in determining the departure figures 
for column 6. The average yield of corn for the period from 
1854 to 1873 was 32.9 bushels to the acre; from 1874 to 1893, 
33.5 bushels to the acre; and from 1894 to 1913, 37 bushels 
to the acre. Inasmuch as a mean yield was determined for 
each twenty years in showing the departure from the normal, 
the rainfall departures in column 3 were obtained for the same 
years in the same manner. It will be noticed also that the 
yield figures are given to tenths while the departure figures 
are to the nearest whole number. 

The figures in column 7 are the square of the departure 
figures in column 6 and correspond with column 4. In col- 
umn 8 there is given the product of the two departure columns 
3 and 6. Care must be taken in this column to place the 
proper sign before the figures, remembering that in multiply- 
ing like signs produce ''plus" and unlike signs " minus '^ 
values. The next step in the calculation is to obtain the sums 
of columns 4 and 7, multiply them and obtain the square root 
of the product. The sum of colmiin 4 is 111.83 and of col- 
umn 7, 1,045. The product of these factors is 116,862.35 
and the square root of this product is 341.8. 

The next step is to obtain the algebraic sum of the values 
in column 8. This is +203.2 and this must be divided by 
341.8, the square root of the product of the sums of columns 



CORRELATION 57 

4 and 7. This gives a quotient of +0.59 which is called the 
"correlation coefficient" or r. 

135. Value of correlation coefficient. — In this method of 
correlation, if there is an exact relation l)etween the two fac- 
tors under discussion, the correlation coefficient will be either 
+ 1 or — 1. That is to say, if every time the rainfall was in- 
creased a certain amount the corn yield was increased in ex- 
actly the same ratio, then the correlation coefficient would 
be exactly +1. And on the other hand if every time the 
rainfall was increased a certain definite amount the corn 
yield would be decreased in an exact ratio, the correlation 
coefficient would be exactly — 1. 

So in this correlation, the nearer the correlation coeffi- 
cient, r, approaches 1 the closer the relation, and the nearer 
it approaches the less the relation. Some writers believe 
that the relation or influence of one factor on another is well 
established if the correlation coefficient is three times the 
probable error, while others think that it should be six times 
the probable error. It probably is safest to assume that there 
may be some relation if the correlation coefficient is three 
times the prot^able error and the relation is established be- 
yond question if it is more than six times the probable error. 

When the correlation coefficient is six times the probable 
error, the chance that there is a relation between the two fac- 
tors is something like 15,000 to 1, and when it is two times the 
probable error it is about 7 to 1. 

136. The probable error. — The probable error is found 
by the following equation in, which r is the correlation coef- 
ficient and n the number of years under consideration: 

1 — r- 
0.674 —yJ- 
Vn 

Substituting the values obtained in Table 3, we have the 
equation : 

1 — (0.59)2 



0.674 



V'60 



which equals =i= 0.057 which is only one-tenth of the correlation 
coefficient. This shows without question a very high corre- 
lation between the July rainfall and the yield of corn in Ohio 
covering a sixty-year record. 



58 AGRICULTURAL METEOROLOGY 

137. Partial or net correlation. — When it is desired to 
determine the influence of each factor where two or more are 
involved, partial or net correlations can be made. A case in 
point would be the weight that should be given to both tem- 
perature and rainfall for any month on the yield of corn. 

In this case there are the three variables, precipitation, 
temperature, and yield, to consider. By representing these 
by p, t, and y respectively and writing rpy, rty, and rpt, to 
represent respectively the correlation coefficients between 
precipitation and yield, temperature and yield, and precipi- 
tation and temperature, the equations may be written as fol- 
lows: 



(1) I-py.fc = 



(2) rty.p = 



rpt rty 



V(l - rpt^) (1 -rty2) 

rty rpt rpy 

V(l - rpt^) (1 - rp/) 



By inserting the various correlation coefficients in these 
equations and making the calculation, there will be in equa- 
tion 1, the influence of the rainfall on the yield of corn after 
eliminating the influence of the temperature and in equation 
2 the influence of the temperature after eliminating the effect 
of the rainfall. The influence of other factors such as sun- 
shine may be obtained in a similar manner. 

138. A graphic illustration of the influence of two factors 
on a third. — Figs. 35, 36, 43, 48, 58, and 59 show a graphic 
method of determining in a general way the combined effect 
of temperature and rainfall on the yield of crops. 

LABORATORY EXERCISES 

1. Paragraph 98. Obtain rainfall, temperature, and crop yield data 
and prepare curves showing relation between two factors. 

2. Paragraph 102. Make dot charts on cross-section or squared pa- 
per, from the climatic and yield data. Place the yield figures on the 
axis of abscissas, or horizontal axis, and the temperature or rainfall 
figures on the axis of ordinates. 

3. Paragraph 108. Calculate the straight line of nearest fit for the 
dot charts made. 

4. Paragraph 113. Calculate the parabola of nearest fit for the dot 
charts made. 



CORRELATION 59 

5. Paragraph 129. Calculate the correlation coefficient for the data 
which have a linear relation as shown by the dot charts made. 

6. Paragraph 13G. Calculate the probable error of the correlation 
coefficient determined. 

7. Paragraph 137. Calculate the partial or net correlation for any 
equation where three factors are involved. For example, temperature 
and rainfall and the yield of a crop. 

8. When three factors are involved, chart the figures showing the 
departures of the temperature and the departures of the rainfall from 
the normal on cross-section paper as in the figures indicated. The loca- 
tion of each "point" is fixed by giving its distance from the vertical and 
horizontal axes. The distance from the vertical axis is called the ab- 
scissa, and the distance from the horizontal axis is called the ordinate, 
of the point. The horixontal axis is commonly called the X-axis, or the 
axis of x; and the vertical axis the Y-axis, or the axis of y. The ab- 
scissa and the ordinates are then called respectively the x and y coordin- 
ates. 

The two axes divide the plane into four parts, called quadrants. 
In working the above it is well to consult one of the text-books on the 
method of least squares. 

REFERENCES 

Elementary Notes on Least Squares, the Theory of Statistics and 

Correlation, for Meteorology and Agriculture. Charles F. Marvin. 

Monthly Weather Review, October and November, 1916. 
Frequency Curves of Climatic Phenomena. H. R. ToUey, Monthly 

Weather Review, November, 1916. 
Introduction to the Theory of Statistics. G. Udny Yule, London. C. 

Griffin & Co., 1912, pp. 188, 208-209, 225-226, and 252. 
Mathematics for Agricultural Students. H. C. Wolff. McGraw-Hill 

Book Co., 1914. 
Method of Least Squares. Mansfield Merriman, New York, 1915. 
On the Systematic Fitting of Curves to Observations and Measurements. 

Karl Pearson, Biometrika, Cambridge, April, 1902, I: 265-303; No- 
vember, 1902, 2: 1-23. 
On the Partial Correlation Ratio. Karl Pearson, London, Royal Society 

Proceedings, Series A, Vol. 91, 1915, pp. 492-498. 
Statistical Methods with Special Reference to Biological Variation, 

third revised edition. C. B. Davenport, New York, J. Wiley & 

Sons, 1914. 
The Practical Application of Statistical Methods to Meteorology. W. 

H. Dines, London, H. M. Meteorological Office. The computer's 

hand-book. 
An Elementary Explanation of Correlation: Illustrated by Rainfall 

and Depth of Water in a Well. R. H. Hooker, Quarterly Journal 

Royal Meteorological Society, October, 1908. 



60 AGRICULTURAL METEOROLOGY 

An Elementary Treatise upon the Method of Least Squares with Numer- 
ical Examples of its Application. George C. Comstock. Ginn & 
Co., Boston, 1889. 

Correlation of Economic Statistics. W. M. Persons, Boston American 
Statistical Association, Quarterly Publications, Vol. 12, 1910, 
pp. 287-322. 

Coefficient of Correlation, The. Wm. G. Reed, Quarterly Publication 
of the American Statistical Association, June, 1917. 

Correlation in Seasonal Variations of Weather. Gilbert T. Walker, I- 
VI. Simla, 1909-1915. r°. (Indian met'l dept. Memoirs.) 

I. (A) Correlation in Seasonal Variation of Climate. V. 20, pt. 6, 
1909, pp. 122. 

II. (B) On the Probable Error of a Coefficient of Correlation with a 
Group of Factors. V. 21, pt. 2, 1910, pp. 22-26. 

Correlation of the Weather and Crops. R. II. Hooker, Journal of the 
Royal Meteorological Society, JVIarch, 1907. 

Elements of Statistical Method. W. I. King, New York, Macmillan, 
1912, pp. 197-215. 

Theory of Correlation as Applied to Farm Survey Data on Fattening 
Baby Beef. PI. R. Tolley., U. S. Department of Agriculture, Bulle- 
tin 504, Washington, Government Printing Office, 1917. 

Theory of Measurements. J. S. Stevens, D. Van Nostrand Co. 1915. 

The Mathematical Theory of Probabilities and its Application to Fre- 
quency Curves and Statistical Methods. A. Fisher. The Macmillan 
Co., 1915. 



CHAPTER V 

CLIMATE AND CROPS 

Climate has been defined as ''mean weather." CHmate is 
the sum total of the meteorological phenomena that charac- 
terize the average condition of the atmosphere at any place 
on the earth's surface. 

139. Solar or mathematical climate has to do with the 
amount of energy received from the sun at the surface of the 
earth. The solar climate of a place, then, depends on its lati- 
tude and the conditions of the atmosphere. 

140. Physical or natural climate is the solar climate as 
modified by the surface features of the earth. The chief 
causes of this modification or interference with the solar cli- 
matic zones are : (1) Irregular distribution of the land and 
water over the earth's surface; (2) atmospheric and oceanic 
currents; (3) difference in altitude of the land above sea- 
level. 

141. Three classes of climate. — Climate then depends on: 
(1) latitude; (2) location with reference to land and water; 
(3) elevation. There are three main classes of climate found 
on the surface of the earth: (1) continental; (2) marine or 
oceanic; and (3) mountain. 

142. Continental and marine climates. — The surface of 
the land warms up more rapidly under the influence of sun- 
shine than the surface of the water, and the land loses heat 
more rapidly at nighttime by radiation than the water. 
Hence, diurnal changes in temperature are much more rapid 
in continental climates in the interior of the country than 
near the coast. Generally the temperature changes are 
greater between summer and winter; so that the common 
feature of a continental climate in all latitudes is a large 
range in temperature. Other things being equal, the range 
is greater the higher the latitude. Over continents the high- 
est temperature comes about one month after the date of the 

61 



62 AGRICULTURAL METEOROLOGY 

sun's maximum altitude. In marine climates the warmest 
month is August, two months after the sun has reached its 
highest point. 

Over continents the minimum 'temperature is one month 
or less later than the time when the sun is farthest south, 
while in a marine climate the lowest temperature does not oc- 
cur until two or even three months after the sun is the lowest. 
A marine climate has a cold spring and warm autumn, April 
and May being colder than September and October. The 
conditions are reversed on the continent, where the spring is 
warm and the autumn cold; April is warmer than October as 
a rule. 

143. Mountain climate. — Mountain systems exert a pro- 
found influence on chmate, not only in the immediate neigh- 
borhood, but also far to the leeward with respect to the 
prevailing winds. In general the characteristics which dis- 
tinguish between the climate of mountains and the surround- 
ing lowlands are: (1) lower temperatures in both winter and 
summer; (2) a drier atmosphere; (3) a greater rainfall and 
snowfall on the slopes exposed to the moisture-laden winds; 
(4) higher wind velocities; and (5) greater intensity of the 
direct solar rays. 

An interesting and peculiar climatic condition of moun- 
tains is the low night temperatures in the valleys as compared 
with the surrounding hillsides, and the early frosting of all 
crops in the valleys. In the Alps this fact is recognized and 
farm-houses and villages are often built on the hillsides in- 
stead of in the valleys. During the calm clear spells of late 
autumn, the traveler stopping at one of these houses on the 
steep hillside may there breathe the air that has the mild- 
ness of summer; he may see the green fields still decked with 
autumn flowers, and may watch the sheep grazing in the 
fields, while down below in the valley the ground is already 
frozen hard, the trees are leafless, and all activities of plant 
life have long since ceased. 

144. Verdant zones or thermal belts. — In North Carolina 
there are rather poorly defined zones along the mountain side 
called thermal belts where the damage by frost is practically 
nil, while above and below this belt crops may be killed. A 
careful investigation by the Weather Bureau and the State De- 
partment of Horticulture shows, however, that this frost- 



CLIMATE AND CROPS 63 

free zone is variable and fluctuates up and down the mountain 
side with cUfferent seasons. 

145. Climatic zones. — For more than two thousand years 
geographers have recognized three cHmatic divisions, torrid, 
temperate, and frigid. These are purely astronomical and 
are really zones of sunshine. In the tropics the sun reaches 
the zenith twice each year and the da}^ is never less than ten 
and one-half hours long. In the frigid or polar zone, the sun 
is below the horizon for twenty-four hours at least once in 
winter, and above once in summer. The temperate zone is 
between the two extremes. At no point can the sun be 
in the zenith, nor, except on the polar circle, is there any- 
where a twenty-four hour day or night. Early writers 
taught that both the torrid and frigid zones were unin- 
habitable. 

146. Relative areas and limits. — Taking the area of a 
hemisphere as unity, the relative areas of these zones are: 
tropical, 0.40; temperate, 0.52; and polar, 0.08. Inasmuch 
as temperature determines habitability, the limits of plant 
growth, and the general conditions of human life, one impor- 
tant division of climate has been made in limiting the temper- 
ate zone within certain well-fixed limits of temperature, these 
limits having well-marked relations to organic life. Two 
critical daily mean temperatures, 68° and 50°, and the dura- 
tion of these periods for one, four, and twelve months are the 
factors of this classification. A normal duration of 50° for less 
than a month fixes very well the polar limit of trees and the 
limits of agriculture. Near this line are found the last group 
of trees in the tundras. A temperature of 50° for four months 
marks the limit of oaks and closely coincides with that of 
wheat cultivation. North of the tree limit, agriculture 
ceases and man's food is to be sought very largel}- from the 
sea. With approach to this line, the period of plant growth 
is shortened more and more, agricultural operations become 
restricted, and occupations of other kinds are taken up. 

From this classification we have: (1) tropical belts with 
all months hot, that is, the temperature averaging over 68°; 
(2) temperate belt with the mean temperature of four of the 
twelve months averaging between 50° and 08°; (3) polar belts, 
that is, with all months cold, or with the average tempera- 
ture for the warmest month 50° or lower. 



64 AGRICULTURAL METEOROLOGY 

147. The main factors in climate. — The main meteoro- 
logical factors in determining chmate are temperature, mois- 
ture, sunshine, and wind. 

TEMPERATURE 

148. Importance. — The temperature is the most impor- 
tant factor in determining the flora and the general zones of 
vegetation and the location of the most important food plants. 
Experiments indicate that the higher forms of plants cannot 
grow where the temperature remains continuously below 32° 
or above 122°, while most food plants can thrive only within 
much narrower ranges. Wheat and corn are grown within a 
belt where the mean annual temperature is between 39° and 
68°; oats and barley, 28° to 68°; rice, 68° to 86°: and pota- 
toes 35° to 61°. 

149. Temperature effects. — High and low temperatures 
affect crops in various ways, but the principal ones are by 
preventing germination, checking growth, killing all or part 
of the vegetative parts, injuring the blossoms, or damaging 
the maturing products. Most plants make growth only dur- 
ing the portion of the year when the temperature remains 
within certain limits, maturing, dying, or becoming dormant 
when the temperature falls too low or rises too high. 

150. Temperature and plant distribution. — So far as the 
controlling influence of temperature is concerned, plants 
spread readily to the east and west, less readily to south and 
least easily to north. 

151. Affects various plants differently. — Most annuals 
grow continuously during a certain period of the year and 
either die or mature when it becomes too cold or too warm. A 
few become dormant when unfavorable temperatures obtain, 
resuming and finishing growth when more favorable temper- 
atures prevail. 

152. Periods of growth. — For the sake of convenience, 
the months when the mean daily temperature is between 49° 
and 72° are considered periods of growth for most crops. 
When the average temperature is above 72° and there is 
plenty of moisture, tropical and subtropical plants continue 
growth or fruits will ripen. When moisture is lacking, how- 
ever, this becomes a period of summer rest. 

153. Periods of rest. — In most sections of the United 



CLIMATE AND CROPS 65 

States, there are periods during the year, varying in length 
in different locaUties, with temperature too low for active 
plant growth; these are known as rest-periods. When the 
temperature in its annual march rises to the vegetative or 
active value, growth, in general, begins. The rate is slow at 
first, but it is accelerated with the rise in temperature, pro- 
vided sufficient soil-moisture is present, until the optimum 
is reached, after which growth is slowly retarded until the 
winter rest-period is again entered. The rest, vegetative, and 
optimum temperature values differ for different plants and 
localities, but, in general, cultivated plants remain more or 
less dormant in temperate climates as long as the mean tem- 
perature remains below 49°. 

154. Length of rest period. — Fig. 18 shows the general 
rest-periods for most plants in different sections of the coun- 
try, as determined by the average time in months between 
the first month in autumn and the last in spring, inclusive, 
with a mean temperature below 49°. The vegetative period 
is represented by the months of the year other than those 
shown for the several areas on the chart. 

In portions of the northeastern states, in the western Upper 
Lake region, most of Wisconsin and Minnesota, and also in 
the Dakotas, Montana, and the central and northern por- 
tions of the Rocky Mountain region, the rest-period extends 
from October to April, or is of seven months' duration. Im- 
mediately to the southward of this area, there is a belt of 
limited width in which the mean temperature does not fall 
below 49° until November, but remains below that value in 
spring for the month of April, thus covering a period of six 
months. Throughout a wide belt, extending from Kansas 
and Nebraska eastward to the middle Atlantic coast and 
reaching as far south as the northern portions of North Caro- 
lina, Tennessee, Arkansas, and Oklahoma, the rest-period ex- 
tends from November to March, five months. From this 
area it decreases southward to the central portion of the Gulf 
states where only one month, January, has a mean tempera- 
ture below 49°; while along the Gulf coast, including the 
whole of Florida, a mean monthly temperature of 49°, or 
higher, is found in every month. 

Owing to the diversity of topography from the Rocky 
Mountains westward, very little detail has been attempted in 



66 



AGRICULTURAL METEOROLOGY 




CLIMATE AND CROPS 67 

drawing the chart, and consequently the areas shown for 
these regions are broadly generalized. However, the dormant 
period is mostly from six to seven months in length, except 
in part of the Pacific Coast states and in the lower Colorado 
River Valley where in some areas the monthly means do not 
fall below 49°. 

155. Effective temperatures. — There is a certain definite 
temperature below which a plant will make no growth. This 
temperature, which may be called the "zero of vital tempera- 
ture" varies with different species and may vary with 
varieties of the same species. It varies also with differ- 
ent functions of the same plant. The difference between this 
"zero" and the prevailing temperature is termed the "effect- 
ive temperature." If the zero temperature is 46°, and the 
prevailing is 48°, the effective temperature is 2°. There is 
also a certain temperature above which there will be no 
growth. 

156. Temperature and carnations. — It is stated that the 
temperature in greenhouses during the growth of carnations 
should be kept as near as possible at 50° to 53° at night, and 
between 60° and 62° during the day. Some growers advocate 
even slightly lower temperatures for best results. Because 
the air temperatures frequently run higher than this, it is not 
practicable to raise carnations commercially in the extreme 
South. 

157. " Zero " of vital temperature point 6° C. (42.8° F.).— 
The actual temperature at which a plant begins to carry on 
its functions varies with different species and the climate to 
which it has been subjected. Some species of the lower forms 
of plants will grow at freezing or slightly below, while date- 
palms, for example, make little or no growth below 64°. It is 
believed, however, that 6° (C.) or 42.8° (F.) marks the tem- 
perature below which most field and garden crop plants will 
make little if any development. Hence, the "zero" of vital 
temperature ma}^ safely be taken as 43° F. in whole numbers. 

158. A new " zero '* suggested. — Kincer has recently 
suggested that the zero of vital temperature for the spring 
seeded crops should be the mean daily temperature at the 
average date of the beginning of planting. It has been found 
that these temperatures for some of the important crops are 
as follows: 



68 AGRICULTURAL METEOROLOGY 

Spring wheat, 37° to 40° 
Oats, 43° 

Potatoes, 45° 

Corn, 55° 

Cotton, 60° to 62° 

The normal or seasonal rise in temperature in the spring is 
quite regular, and reaches the points indicated above on later 
dates at higher latitudes. The average date of the beginning 
of planting progresses also toward the north (in the north- 
temperate zone), and the average date of seeding agrees with 
the temperatures indicated above in different latitudes. 

159. Total effective temperatures. — For many years an 
effort has been made to determine the total of the effective 
heat necessary for any definite phenological period in crop 
development. There has been a difference of opinion as to 
the temperature from which the calculations should be made; 
whether this temperature should be that recorded in the sun 
or in the shade; whether it should be the daily mean temper- 
ature or the maximum temperature; whether it should be 
calculated from the date of seeding or from the date that the 
plant appears above the ground, or in the case of winter grains 
whether it should be from January 1 or some date in the 
spring; in the ca^e of fruits, from some definite date of the 
preceding year or at the opening of spring, and after these 
points have been determined to the personal satisfaction of 
the investigator, how the effective temperature should be 
calculated. 

The best zero point of growth seems to be 43° and all daily 
mean temperatures above this point, with the thermometers 
exposed in the standard shelter, may be considered as effect- 
ive temperatures. 

160. Summation processes. — Three methods have been 
used to determine the effect of temperature above the zero 
values on plant growth. The " remainder " process, the " expo- 
nential system," and the "physiological simimation indices." 

161. The remainder indices. — By this process, which has 
been used most frequently, all mean daily temperatures above 
the zero temperature are added together. For example, if the 
mean daily temperature between certain phenological events, 
such as the date of planting corn and the date when it comes 
into blossom, is 65°, the zero temperature of 43° is subtracted 



CLIMATE AND CROPS 69 

from 65° and the remainder multiplied by the total number 
of days between the two dates. Or the difference between 
43° and the mean temperature is determined for each day be- 
tween the two events and these remainders added together. 
Other influences being similar, it is argued that the sum of 
these daily differences would be the same for different sea- 
sons for the same variety of plants. Elaborate studies have 
been made in Europe and the results seem to bear out the 
theory in a general way. The total of these differences has 
been much the same in the same latitudes and with equal ele- 
vation. ^ With higher altitudes or higher latitudes, the total 
heat units, as these sums are designated, necessary from plant- 
ing to ripening for any crop become less. This is due partly 
at least to longer hours of daylight, shorter growing season, 
and plant characteristics. 

162. Exponential indices. — These are based on the fact 
that the plant growth ratio follows the chemical principle of 
van't Hoff and Arrhenius which states that the chemical re- 
action velocities about double with each increase in tempera- 
ture of 18° (F.). With this law it is considered that the rate 
of growth will be twice as great with a mean daily tempera- 
ture at 79° as at 61°, and four times as great at 97° as at 61°, 
other conditions being the same. 

163. Physiological summation indices. — These indices 
were derived by Livingston from a study by Lehenbauer of 
the relation of temperature to the rate of elongation in seed- 
hng maize shoots. These data showed that the average 
hourly rate of elongation of the maize shoots exposed to main- 
tained temperatures for twelve hours was 0.09 mm. for 12° 
(C); 1.11 mm. for 32° (C), and 0.06 mm. for 43° (C). Maize 
seedlings about 10 to 12 centimeters high were used in this 
test, which had been sprouted practically in darkness and 
with approximately constant temperatures. The seed was 
uniform and of good quality, and so-called "sports" were 
eliminated before the actual temperature influence test was 
begun. The plants were then exposed in a chamber with 
moderate air circulation with an air humidity of approx- 
imately 95 per cent, and with light conditions fluctuating 
between very weak, diffuse daylight and darkness. The incre- 
ments of elongation were measured at three-hour intervals 
for the low and the high temperatures and at longer intervals 



70 AGRICULTURAL METEOROLOGY 

for the remainder, the periods of exposure being from three to 
twenty-one or more hours to maintained temperatures of 
12° (C.) to 43° (C). 

Graphs made from these detailed studies showed clearly 
the existence of the minimum, optimum, and maximum tem- 
peratures for this kind of growth and that the optimum tem- 
perature varies with the period of exposure for which the aver- 
age hourly growth-rate was determined. For a three-hour 
period, the optimum temperature was 9° (C), for a six-hour 
period it was 30° (C), for nine-hour, twelve-hour, and 
twenty-one-hour periods, it was 32° (C.) or 48.2°, 86°, and 
89.6° (F.), respectively. 

The definite results of these studies are given as follows by 
Livingston : 

1. The somewhat widely accepted idea that the curve of growth in 
relation to temperature shows two optima is not at all substantiated in 
this work with the shoots of maize seedlings grown in water culture, 
practically in darkness, and with relative air humidity of 95 per cent. 

2. The optimum temperature for growth of shoots of maize seedlings 
in water culture, for a 12-hour period, is shown to be 32° (C). 

3. The optimum temperature for growth, under these conditions is 
found to change as the length of the period of exposure is altered. 

4. At high temperatures (31° C. and above), for shoots of maize seed- 
lings under these experimental conditions the initial growth-rate is not 
maintained, there being a marked falling off in this rate during pro- 
longed periods of exposure. 

5. This decrease in the growth rate with prolonged periods at high 
temperatures makes it necessary to consider the length of the periods 
for which average growth rates are obtained, in defining the optinmm 
for growth of these shoots. Indeed, it appears that the term "optimum 
temperature" for growth, in this case at least, is quite without meaning 
unless the length of the period of exposure is definitely stated. 

6. The fall in growth rate here brought out is similar to the decrease 
in rate of certain other physiological processes under the influence of 
high temperatures during prolonged periods. 

7. At temperatures near the minimum (12°-14° C.) for the growth 
of shoots of maize seedlings under the conditions here employed, no de- 
crease in the growth rate is shown, even with rather prolonged periods 
of exposure. 

8. The growth rate at medium temperatures accords with the van't 
Hoff law, showing a doubling of the rate for each rise of 8° or 10° (C). 

Great care was taken in all this study, and as laboratory 
test and as a basis for ecological investigations the informa- 



CLIMATE AND CROPS 



71 



tion obtained is of marked value. It must be borne in miad, 
however, that the plants were practically in darkness during 
the entire period of experimentation, and that the study was 
made in only one phase of the development of one plant, and 
care should be taken in applying the results obtained to a 
study of the plants under natural conditions. 



M 


,, / 1 


75 - yi- K 


r-/9 / J ^-^ 


to f- -4-^- -- 

45.-Jr-- -4-- -"" 1 


^^ r ^- r - - - 

30 t-.-.cll.. 1 


/5 ^^"t M -"" 




PeS^C2 4 6 8 /(? /2 /4 /6 /8 20 22 P4 26 28 30 32 34 36 38 4042 44 4<^ 48 



Fig. 19. — Graphs showing increase in value of index of temperature 
efficiency for plant growth (ordinates) with rise in temperature itself 
(abscissas), for the three systems of indices. Graph I represents the 
remainder system, Graph II the exponential one. The broken line is 
Lehenbauer's graph of the relation of temperature to the rate of 
elongation of the shoots of maize seedhngs. The smoothed graph 
corresponding to the latter represents the physiological system of 
indices. All graphs pass through unity at 4.5° C. (F.). 

Fig. 19 is from Livingston and the following is quoted to 
explain the graphs: 

As is shown by Fig. 19 the rate of increase in index value with rise of 
temperature, between the minimum and optimum for growth is much 
more rapid in the case of the physiological series than in that of either 



72 AGRICULTURAL METEOROLOGY 

of the other series. The range of temperature thus indicated (from 2" 
C. or 35.6° F. to about 32° C. or 89.6° F.) is the range usually en- 
countered in nature during the frostless season, at least in temperate 
climates, and most of the plant growth of the world is probably accom- 
plished with temperatures lying within this range. Practically, this very 
rapid rise in the index values constitutes the most important difference 
between the physiological series and the other two. While it is quite 
apparent that the system of physiological indices here described is far 
superior, in several respects, to the other systems heretofore suggested, 
it is equally clear that these indices are to be regarded as only a first ap- 
proximation and that much more physiological study will be required 
before they may be talcen as generally applicable. In the first place, 
they are based upon tests of only a single plant species, maize, and there 
are probably other plants (perhaps even other varieties of the same 
species) for which they are not even approximately true. Second, these 
indices are derived from the growth of seedlings, and no doubt other 
phases of growth in the same plant may exhibit other relations between 
temperature and the rate of shoot elongation, and, third, these indices re- 
fer to rates of shoot elongation and there are many other processes in- 
volved in plant growth, which may require other indices for their proper 
interpretation in terms of temperature efficiency. Fourth, they apply 
strictly only under the moisture, light, and chemical conditions that pre- 
vailed in Lehenbauer's experiments; with more light or with a different 
light mixture, with different humidity conditions, or with different 
moisture or chemical surroundings about the roots, these same plants 
in the same seedling phase, may exhibit very different values of the 
temperature efficiency indices. Fifth and finally, plants in nature are 
never subject to any temperature maintained for any considerable pe- 
riod of time, and these indices are derived from 12-hour exposures to 
maintained temperatures. 

Figs. 20, 21, and 22, show Livingston's climatic zonation 
for the United States by the remainder, exponential, and 
physiological indices, respectively. 

164. Both temperature and moisture. — Livingston has 
carried these applications still further in a paper suggesting 
a method by which the moisture and temperature conditions 
of any locality for any period, as they affect plants, may be 
expressed as a single numerical value, the index of moisture- 
temperature efficiency for plant growth. This index is the 
product of three factors: The index of rainfall, the reciprocal 
of the index of atmospheric evaporation, and the physiolog- 
ical index of temperature efficiency. 

The writer states that the index of moisture-temperature 



CLIMATE AND CROPS 



73 



efficiency as above described may be represented by the for- 
mula 

T — T P 

J-e 

where "I" denotes the efficiency index for the tiaiie period 
considered and the subscript letters denote the respective en- 
vironmental conditions for which the various indices stand. 
lint is the moisture-temperature index with which we are 
mainly concerned. It is the index of temperature efficiency, 




Fig. 20. — Chart of the United States showing climatic zonation ac- 
cording to remainder summation indices of temperature efficiency for 
plant growth, for the period of the average frostless season. 



derived by means of the physiological system. Ip is the in- 
dex of precipitation intensity and represents simply the sum- 
mation of the rainfall for the period. le is the index of the 
atmospheric evaporation, also a simple summation for the 
period. 

165. Weakness of summation plan. — Seeley has shown 
that neither of these systems ajz;ree with the actual tempera- 
tures recorded during the different growing seasons, and that 
the effective temperatures for different years may vary as 



74 



AGRICULTURAL METEOROLOGY 



much as 50 per cent. He found that Livingston's method 
gave the closest comparison during the early stages of corn 
growth if the daily maximum temperatures are used instead 
of the means. 

166. Plant temperatures. — Seeley suggests that the tem- 
perature of the plant should be considered in calculating ef- 
fective temperatures instead of that of the air. He carried on 
a series of observations at Lansing, Michigan, during the 
growing season in 1915 and 1916 in which thrice daily records 




Fig. 21. — Chart of the United States showing climatic zonation ac- 
cording to exponential summation indices of temperature efficiency 
for plant growth, for the period of the average frostless season. 

were kept of the soil, plant, and air temperatures and the 
rate of growth of plants part of the time. 

167. Temperatures of leaves higher in sunshine than air 
temperatures. — Seeley found that when the sun was shining 
the leaf temperature was always higher than the air temper- 
ature, this difference being as great as 20° to even 36° on es- 
pecially clear and still days. In 304 observations made at 
midday, the plant thermometer was lower than the air tem- 
perature only forty-one times and these days were invariably 
dark and cloudy, frequently with rain falling. 



CLIMATE AND CROPS 



75 



168. Leaves cooler at night. — In the early morning, the 

temperature of the leaves was about 3° to 4° cooler than 
the air temperature and the plants lost their heat more 
rapidly than the air, in the early evening. At 7 p. m., 
the leaves were sometimes 9° or 10° cooler than the 
air. 

169. Effect of cloudiness on plant temperature. — Seeley 
tabulated a total of over 300 days and found that the plant 
temperatures averaged 15° higher than the air temperatures 



g9 /£? /^s/J■J/^/ //s J/7 iisiij /// 109 /oviasm m 99 9? 9S 93 9/ es er^sj s/ 79 77 7S 73 7/ 69 67 es 




IZI //9 117 l/S //3 I/I 109 107 /OS ,03 10/ 99 97 SS' 93 3/ 3987 SS 83 6/ 79 77 7^73 



Fig. 22. — Chart of the United States showing climatic zonation ac-' 
cording to physiological summation indices of temperature efficiency 
for plant growth, for the period of the average frostless season. The 
numbers on the isoclimatic lines each represent thousands. Broken 
lines denote a very high degree of uncertainty. 

in full sunshine, in partial sunshine 10°, and in cloudy 
weather nearly 1°. From these averages he deduced the fol- 
lowing formula for finding the effective temperature from 
air temperature: T = t+15C-|-10P, in which T is the 
sum of effective temperatures for plant growth, t is equal to 
m-42x, m being the sum of all maximum temperatures 
above 42° during the period in question; x the number of such 
days; C, the niunber of clear days, and P, the number of 
partly cloudy days during the period. 



76 AGRICULTURAL METEOROLOGY 

170. Difficulty of comparing plant temperatures. — The 

difference in the temperature of plants in direct sunshine and 
in shade, and the action of the pigments in varying the tem- 
perature of different colored leaves and plants in sunshine, is 
shown in a recent article by the French naturalist J. Du- 
frenoy, of the Biological Station at Arachon, in the Revue 
Generale de Sciences. 

He explains the formation of the pigments in plants, and 
the increase or decrease of pigmentation in varying heat, 
moisture, and sunshine values, then shows the effect of these 
different pigments in the absorption of solar energy. 

The following is quoted from a review of this article in the 
"Scientific American Supplement" for February 15, 1919: 

The solar energy absorbed by the pigments is largely converted into 
heat. In January at Arachon, on a fine day, the temperature of the 
plants exposed to the sun exceeds that of the air by from 6° to 8° C, at 
noon, and by from 12° to 15° C. at 3 p. m.; the amount of this rise in 
temperature varies according to the color and to the intensity of the 
pigmentation, so that a difference of more than one degree C. may exist 
between the j^ellow and the green leaves of the variegated foliage of a 
spindle tree, or even between the two borders of a single variegated leaf. 
Experiments made in January at Arachon gave the following results: 

In a variegated leaf of the Iris pallida the green portion showed a rise 
in temperature of 9.8° C. over that of the air against a rise of only 8.5° 
C. in the yellow portion. Similar observations were made with the red 
and green leaves of an arbutus, the time being 10 a. m., and the temper- 
ature of the air 10° C; in this case the red leaf showed a rise of 7.5° C, 
and the green leaf a rise of only 7° C. 

In November, tests were made at 2 p. m., with red and white arbutus 
berries, the temperature of the latter being 29.5° C, and that of the red, 
one degree higher. Finally, experiments were made with grapes of va- 
rious colors placed in sunshine and in shade. The temperature of the 
red grapes in the sun was 37° C, and 10° C. less in the shade; that of 
white, green, and amber colored grapes was 34° C. in the sun, and 26° 
C. in the shade. 

A second experiment showed that grapes with a dull surface had a 
temperature of 35.5° C. in the sun, whereas that of those with a bright 
surface was 34.8° C. A highly interesting fact is that every rise of 10° 
C. in the temperature of the organs exposed to sunlight doubles or even 
trebles the rapidity of the reactions observed — for example, the inten- 
sity of respiration is greatly enhanced, more carbon dioxide being liber- 
ated. In fruits exposed to sunlight the plant acids contained are re- 
duced, and the ripening is correspondingly hastened. 



CLIMATE AND CROPS 77 

These experiments illustrate the difficulty in making com- 
parable records of the temperature of plants in sunshine as 
conducted by different investigators or by the same man at 
different times. 

171. Leaf temperature fluctuation rapid. — The use of a 
very sensitive electrical apparatus for measuring the surface 
temperature of leaves shows a very rapid fluctuation of a leaf 
growing in the open. If a moderately strong wind is blowing, 
the temperature may fluctuate as much as 5° C. in thirty 
seconds. 

172. Value of temperature summation figures. — Botan- 
ists have been able to make little practical use of the large 
amount of effective temperature summation data that has 
been compiled, due partly to the difficulty of comparing dif- 
ferent observations. While all of the methods proved, as well 
as the factors presented by various investigators to explain 
the modification of physiological constants, applicable in 
certain circumstances, they are all subject to some exceptions. 

173. Solution possible. — The actual determination of 
some of the physiological constants is possible; in other cases 
certain definite factors can be found which will be of service 
within certain limits. The problem is to devise some method 
for calculating the heat requirements of various crops during 
different periods of development. 

174. Lissner's law. — Lissner developed a theory or law 
which is useful in determining a constant for several locali- 
ties in different latitudes. His law may be stated briefly as 
follows: In two different localities the sums of the effective 
daily temperatures for the same phase of vegetation are pro- 
portional to the annual sum total of all effective temperatures 
for the respective localities. It is a well known fact that plants 
of the same species develop under a considerably smaller sum 
of heat in northern than in southern districts. The Burbank 
plum, for example, blossoms in the middle of March in the 
southern part of the United States and the middle of May in 
the northern portion, while the total effective heat received 
is considerably less in the northern latitude. 

175. Lissner's aliquot. — Lissner's conclusion was that 
this is due to a matter of adaptation to climatic environ- 
ment. That as plants at the southern latitude are subject 
to a much greater sum total of temperature for the entire 



7409 


.130 


7044 


.129 


5578 


.129 


5292 


.109 



78 AGRICULTURAL METEOROLOGY 

year, they simply lengthen all the phases of development in 
the South. Thus the blossoming phase of the Burbank plum, 
as an illustration, depends on a^ constant aliquot, instead of 
depending on a constant temperature sum. 

To compute the aliquot, the sum of the effective tempera- 
tures for a certain phase of development is divided by the 
sum of the effective temperatures for the entire year. The 
determination of the aliquot is illustrated in the following 
for the Burbank plum: 

Sum of temperatures 
Place above 32° from From Jan. 1 to Dec. 31 Aliquot 

Jan. 1 to blossoming 
StiUwater, Okla. 967 

Parry, N. J. 909 

State College, Pa. 725 

Burlington, Vt. 577 

Except at Burlington the proportion is practically the 
same. 

176. Optimum conditions. — It is found that for each 
phase of plant development there is a definite optimum of tem- 
perature, moisture, and light, at which the growth and de- 
velopment goes on with greatest vigor. When either one of 
these factors varies, the effect of the others is changed and 
the development slows down so that the absolute amount of 
heat necessary to complete a definite phase of growth varies 
one year with another, due to the variation of other condi- 
tions. 

177. Time factor. — Another factor of importance is the 
length of time that the plant is subjected to different temper- 
atures. All these conditions can be controlled in a laboratory 
experiment, but are constantly varying in natural growth. 

SOIL TEMPERATURE 

The temperature of the soil affects the germination and 
growth of plants and the development of some plant diseases 
to a marked degree. The temperature of the surface soil va- 
ries with covering, physical structure, moisture-content, in- 
clination, slope, latitude, color, cloudiness, season, tempera- 
ture of the air above, and the like, and efforts to relate soil 



CLIMATE AND CROPS 79 

temperature with plant development must take all these 
things into account. 

178. Most favorable temperature. — It has been found 
that, with other conditions favorable, staple crops will grow 
when the temperature of the soil is as low as 40° and as high 
as 120°. The most favorable temperature for growth is be- 
tween 65° and 70°. The warmer the soil in the spring, the 
more rapid the germination and growth. Soil bacteria do not 
become active until the temperature of the soil reaches 45° 
to 50° F. 

179. Source of heat. — The sun is the chief source of heat 
in raising the temperature of the soil, although a slight 
amount of heat is received from the interior of the earth. 

180. Loss of heat. — The heat that is accumulated -in the 
surface of the earth by absorption of solar energy, is lost by 
radiation through the air to space, conduction to the air above, 
and conduction to lower layers of soil. 

181. Diurnal changes in temperature. — The diurnal 
changes in temperature of the soil usually extend to a depth 
of only about 2 to 3 feet, and these changes occur in the form 
of waves. The surface soil loses heat by radiation very rap- 
idly during the nighttime and reaches its lowest temperature 
just about sunrise. At this time the lowest temperature is 
at the surface and the temperature increases with depth al- 
though losing heat by conduction upward. As soon as the 
surface of the soil begins to absorb solar energy, its tempera- 
ture rises, and in turn begins to warm the next lower layers 
of soil by conduction. This wave of higher temperature fol- 
lows the wave of falling temperature, both decreasing in 
range as they travel downward. 

As late afternoon approaches again and the surface loses 
heat by conduction and radiation more rapidly than it gains 
by absorption, it begins to cool and a second wave of falling 
temperature follows the daytime warmer wave. 

182. The lag in temperature fluctuation. — The lag of the 
maximum and minimum epochs or waves is proportional to 
the depth. The maximum temperature at the surface of the 
ground is about the middle of the afternoon on an average. 
At a depth of 3 to 6 inches, the maximum occurs in the even- 
ing, and at about 1 foot not until the next morning. Below 
this depth the change is slight, but where it does occur, it is 



80 AGRICULTURAL METEOROLOGY 

not until the next day, when a second wave of higher temper- 
ature is starting from the surface. 

183. Annual ranges. — The annual change in temperature 
in the soil is limited to the surface 30 to 40 feet. These 
changes are propagated downward by successive waves in the 
same general way as the diurnal changes. For each step 
downward of 4 feet, the occurrence of the epoch of extreme 
temperature is retarded on an average of twenty-one days. 
The lowest temperature at the lowest depths occurs the fol- 
lowing summer, and the highest the following winter. At a 
depth of 30 to 40 feet, the temperature is at all times about 
the same as the mean annual air temperature. 

184. Soil cover. — While therovis very little difference in 
temperature between cultivated and uncultivated soils, there 
is a marked difference between a bare soil and one covered by 
vegetation. In a four-year study in Michigan it was found 
that the bare ground warms up more quickly in the spring 
and remains at a higher temperature than that covered by 
sod through the summer. In the fall the bare ground loses 
its heat more rapidly and remains colder during the winter. 

185. Snow cover. — A thick snow cover is a most efficient 
agent for keeping the soil warm in the winter and preventing 
it from attaining extreme low temperatures during severe 
cold weather. 

186. Desirability of soil temperature records. — The im- 
portance of a systematic soil temperature survey is well rec- 
ognized. The Ecological Society of America recommends the 
use of soil thermographs, carefully calibrated and with the 
bulb at a uniform depth of 3 inches in level or nearly level 
ground where it is not subject to inundation or saturation. 
The location of the instrument should be where no shade falls 
on the soil at any time and under a light cover of weeds or 
short grass. Temperatures at depth of 1, 5, 12, and 24 inches 
should be recorded also if practicable. 

PRECIPITATION 

After temperature the next most important climatic fac- 
tor is the moisture, either as water-vapor or as water in the 
form of rain, snow, and the like. The rainfall determines the 
productiveness of a country. In places where the tempera- 
ture and sunshine are generally sufficient, the development 



CLIMATE AND CROPS 



81 




82 AGRICULTURAL METEOROLOGY 

of the plants and more especially the crop yields depend most 
largely on the rainfall. 

187. Distribution of precipitation. — The rainfall of the 
whole globe, including both land and water areas, is estimated 
to be about 60 inches a year. The proportion of the land 
areas receiving the different rainfall amounts is indicated by 
the following: 



Annual 


Character of 


Proportion of land 


precipitation 


climate 


receiving 


Less than 10 inches 


arid 


25.0 per cent 


From 10 to 20 " 


semi-arid 


30.0 " " 


a 20 " 40 " 


sub-humid and humid 


20.0 " " 


" 40 " 60 " 


humid 


11.0 " " 


" 60 " 80 " 


<< 


9.0 " " 


" 80 " 120 " 


(t 


4.0 " " 


" 120 " 160 " 


tc 


0.5 " " 


Above 160 " 


11 


0.5 " '' 



This shows that 55 per cent of the land surface of the globe 
receives less than 20 inches of rain a year, while only 25 per 
cent receives over 40 inches. The significance of this must 
be realized when it is remembered that it takes about 2 tons 
of water to produce an ordinary loaf of bread, and that 5-acre 
feet of water are necessary to support one human life. 

188. Precipitation in the United States. — Fig. 23 shows 
the average annual precipitation (rain and melted snow) in 
the United States. The greatest amount is received on the 
North Pacific coast, while the least is in southwestern Ari- 
zona, southeastern California, and western Nevada. 

Fig. 24 indicates the percentage of the annual precipita- 
tion that occurs during the growing season, April to Septem- 
ber, inclusive. 

189. Quantity of water. — The amount of water that falls 
on each acre of ground when rain occurs is shown by the 
following: 



Depth of rain 


Gallons 


Tons per acre 


in inches 


per acre 


{2,000 lbs.) 


0.01 


271.5 


1.1 


0.05 


1,358 


5:6 


0.25 


6,789 


28.0 


1.00 


27,154 


113.0 


5.00 


135,772 


665.0 



CLIMATE AND CROPS 



83 




84 AGRICULTURAL METEOROLOGY 

190. Drought. — A drought may be defined as a condition 
under which plants fail to develop and mature properly be- 
cause of an insufficient suppl/ of moisture. Just what de- 
ficiency of rainfall or how long a period without rainfall or 
with an amount insufficient to cause an appreciable increase 
in soil-moisture will cause a damaging drought, cannot well 
be stated. It will depend on the season of the year, the pre- 
vailing temperature, wind, and sunshine, the kind of plants, 
their critical period of growth, soil texture, moisture in the 
soil at the beginning of the period of deficient rainfall, and 
other factors. 

In Russia a drought has been defined, for convenience, as a 
period of ten days with a total rainfall not to exceed 5 mm. 
(0.20 inch). One definition used in the United States is a 
period of thirty days or more in which the precipitation does 
not amount to 0.25 inch in any twenty-four hours. These 
definitions are purely arbitrary, however, and would not ap- 
ply at all in some places or at all seasons. 

In some parts of the country, a drought may result when 
there are several successive five-day periods with the evap- 
oration from a free water surface in excess of the rainfall. 

191. Rainfall and plant growth. — There was a time when 
water was thought to be the real food of plants, but with 
experiments it became obvious that the influence of rainfall 
on plant growth is exerted in replenishing the moisture in the 
soil. Someone has likened the soil to a gigantic reservoir 
which is replenished at more or less infrequent intervals and 
which is drained by underground seepage, surface evapora- 
tion, and by transpiration of plants. 

A plentiful water supply as a rule favors the development 
of the vegetative organs, while the scarcity of water brings 
about their reduction. On the contrary, the production of the 
sexual organs is usually favored by a lack of water and im- 
peded by an excess. The amount of moisture in the soil af- 
fects the activity of soil bacteria. 

192. Soil-moisture. — The direct source of the water sup- 
ply of plants is moisture in the soil. Probably no other fac- 
tor so often limits crop production as does soil-moisture, as it 
is the means by which the food in the soil is made available 
to the plant. There is no direct relation between the percent- 
age of water present in the soil and the amount that is avail- 



CLIMATE AND CROPS 85 

able for plant use. A sandy soil with 15 per cent of moisture 
may be near saturation and have a large amount of available 
water, while a stiff clay with 15 per cent of moisture may have 
so little available water that all plants will wilt in it. 

193. Wilting coefficient.— The wilting coefficient of a soil, 
as defined by Briggs and Shantz, is the moisture-content of 
the soil (expressed as a percentage of the dry weight) at a 
time when the leaves of the plant growing in that soil first 
undergo a permanent reduction in their moisture-content as 
a result of a deficiency in the soil-moisture supply. 

The water-content of a soil which is available for growth is 
the difference between the actual moisture-content and the 
wilting coefficient. There is a wide difference in the wilting 
coefficient of different soils, as fine soils are much more re- 
tentive of moisture than coarse, while the wilting coefficient 
for any soil is practically the same for all crops. 

194. Transpiration is the term used to express the loss of 
water from the surface of the aerial parts of plants. It is 
often called ''evaporation,'' but is not exactly the same thing, 
even though the rate of each is affected by similar weather 
conditions. Kiesselbach has found that the amount of water 
transpired from a given leaf-area of corn (based on expanse 
of leaf and not on both surfaces) is approximately one-third 
as great as the evaporation from a free water surface of the 
same area. 

The maximum transpiration is at the warmest part of the 
day. On days of extreme temperature there may be an at- 
mospheric demand of ten pounds of water from a single corn 
plant during twenty-four hours. The greater part of this 
need is for a period of about seven hours in the hottest part 
of the day; such days are very critical if there is not moisture 
enough in the soil to supply the demand. Corn curls and 
wilts when the transpiration exceeds the absorption through 
the roots. The plant itself apparently has power to influence 
the rate of transpiration, but outside of the plant influence, 
transpiration increases with increase of temperature and wind 
velocity and decreasing relative humidity. 
^ 195. Evaporation. — The loss of soil-moisture by evapora- 
tion is an important factor especially in dry regions. The 
amount of water evaporated from a free water surface in dif- 
ferent parts of the country is shown in the following tables: 



86 



AGRICULTURAL METEOROLOGY 



AVERAGE WARM-SEASON EVAPORATION 
Table 4. — Summary of Measurements, in Inches, made by the 
Office of Biophysical Investigations, United States De- 
partment OF AGRICULTURE 





Num- 














Aver- 


i 


ber oj 














age 


Station ; 


years 


April May 


June 


July 


Au- 


Sev- 


total, 




in 










gust 


tem- 


April 


record 












ber 


to Sept. 


Yuma, Ariz. 


9 


7.76 


9.54 


10.58 


10.21 


9.61 


7.43 


55.13 


Biggs, Cal. 


4 


4.47 


6.25 


8.64 


9.60 


8.15 


6.38 


43.49 


Akron, Colo. 


10 


4.96 


6.40 


7.88 


9.09 


7.87 


6.48 


42.68 


Aberdeen, Idaho 


6 


4.61 


6.07 


8.46 


9.65 


7.70 


5.58 


42.07 


Colby, Kans. 


4 


4.35 


5.90 


7.48 


8.69 


7.47 


6.02 


39.91 


Garden City, Kans. 10 


6.50 


8.58 


9.89 


10.91 


9.51 


7.46 


52.85 


Hays, Kans. 


11 


6.16 


7.04 


8.42 


9.97 


9.29 


7.02 


47.90 


Crowley, La. 


7 


4.85 


5.69 


6.18 


5.72 


5.36 


4.54 


32.34 


Havre, Mont. 


2 


3.28 


5.51 


5.55 


7.98 


6.40 


3.88 


32.60 


Huntley, Mont. 


7 


3.24 


4.56 


5.89 


7.55 


6.67 


4.32 


32.23 


Moccasin, Mont. 


9 


3.83 


4.93 


5.56 


6.78 


7.06 


4.62 


32.78 


Mitchell, Nebr. 


7 


4.83 


6.16 


7.43 


7.97 


6.80 


5.26 


38.45 


North Platte, Nebr. 11 


5.68 


6.55 


8.14 


9.11 


8.06 


6.11 


43.65 


Fallon, Nev. 


10 


6.21 


8.09 


9.92 


10.78 


9.74 


6.58 


51.32 


Tucumcari, 


















N. Mex. 


6 


7.23 


9.72 


10.89 


10.84 


9.26 


7.44 


55.38 


Dickinson, N. Dak. 10 


4.04 


4.64 


6.25 


6.80 


5.98 


4.08 


31.79 


Edgeley, N. Dak. 


11 


3.60 


4.71 


5.30 


6.40 


5.53 


4.02 


29.56 


Hettinger, N. Dal^ 


:. 7 


4.16 


4.93 


6.40 


7.45 


5.91 


3.92 


32.77 


Mandan, N. Dak. 


5 


3.78 


5.15 


6.06 


7.37 


6.45 


4.49 


33.30 


Williston, N. Dak 


. 8 


4.31 


5.52 


6.39 


7.08 


6.05 


3.76 


33.11 


Lawton, Okla. 


3 


6.60 


6.65 


8.48 


8.97 


8.20 


6.66 


45.56 


Woodward, Okla. 


4 


6.38 


7.51 


9.43 


10.84 


8.54 


6.82 


49.52 


Burns, Oreg. 


4 


3.84 


5.76 


7.29 


9.27 


8.49 


5.68 


40.33 


Hermiston, Oreg. 


6 


4.03 


5.48 


7.47 


8.47 


6.82 


4.38 


36.65 


Moro, Oreg. 


7 


4.54 


6.27 


8.01 


9.35 


8.54 


4.28 


40.99 


Ardmore, S. Dak. 


5 


3.81 


5.24 


7.21 


8.71 


7.56 


6.08 


38.59 


Newell, S. Dak. 


10 


4.23 


5.57 


6.99 


8.43 


6.93 


4.85 


37.00 


Amarillo, Tex. 


11 


7.03 


8.79 


10.17 


10.38 


9.11 


7.23 


52.71 


Big Springs, Tex. 


3 


7.40 


10.03 


12.72 


11.65 


9.88 


7.32 


59.00 


ChilHcothe, Tex. 


5 


6.48 


7.90 


8.98 


10.14 


9.11 


6.30 


48.91 


Dalhart, Tex. 


10 


7.49 


9.52 


10.56 


10.61 


9.63 


7.58 


55.39 


San Antonio, Tex. 


11 


5.70 


6.69 


8.69 


9.61 


9.01 


6.35 


46.05 


Nephi, Utah, 


10 


4.56 


6.16 


8.78 


9.52 


9.23 


6.36 


44.61 


Archer, Wyo. 


5 


3.65 


5.06 


7.17 


7.95 


6.88 


5.63 


36.34 


Sheridan, Wyo. 


1 


3.14 


4.91 


5.82 


9.81 


7.85 


5.14 


36.67 



CLIMATE AND CROPS 87 

Table 5. — Summary of Evaporation Measurements, in Inches, 

MADE BY THE WeATHER BuREAU 



No.q 


/ 












Total 


Station years 


Api^il May 


June 


July 


Aug. 


Sept. 


April 
















to Sept. 


Silverhill, Ala. 1 


4.50 


5.75 


6.90 


5.33 





4.45 





Mesa, Arizona 2 


7.58 


9.20 


10.48 


9.98 


8.58 


6.70 


52.52 


Roosevelt, Arizona 3 


8.05 


10.93 


14.00 


12.81 


11.29 


9.82 


66.90 


Willcox, Arizona 2 


10.82 


11.80 


11.87 


10.96 


9.43 


9.53 


64.41 


Yuma, Arizona 2 


8.04 


9.32 


9.80 


10.55 


10.74 


7.89 


56.34 


Oakdale, Cal. 1 


6.21 


9.07 


14.23 


13.94 


12.67 


5.65 


61.77 


Tahoe, Cal. 3 


2.42 


3.16 


4.38 


5.62 


6.00 


4.89 


26.47 


American University, 
















Dist. of Columbia 3 


4.64 


6.06 


6.23 


6.50 


5.82 


4.22 


33.47 


Lawrence, Kansas 3 


5.25 


7.08 


8.99 


10.47 


9.52 


5.44 


46.75 


Columbia, Missouri 3 


4.40 


5.97 


7.55 


9.51 


7.68 


5.14 


40.23 


Bozeman, Montana 3 


2.10 


5.12 


7.46 


8.52 


7.44 


4.16 


34.80 


Valver, Montana 3 


3.54 


6.16 


8.65 


6.51 


7.52 


3.94 


36.32 


Tiincoln, Nebraska 2 


5.76 


7.44 


9.92 


10.32 


9.54 


6.44 


49.42 


Elephant Butte Dam, 
















New Mexico 3 12.12 


14.89 


15.47 


12.87 


10.99 


9.43 


75.77 


Santa Fe, New Mex.3 


6.68 


8.71 


11.28 


9.15 


8.05 


6.98 


50.85 


Albany (near), 
















N. Y. 2 


1.70 


4.86 


4.74 


5.60 


5.88 


3.40 


26.18 


Wooster, Ohio 3 


3.35 


4.88 


5.34 


6.04 


5.99 


3.78 


29.38 


Rapid City, S. D. 3 


2.99 


5.20 


6.55 


8.19 


7.16 


5.15 


35.24 


HiUs Ranch, Texas 3 


6.74 


7.52 


9.36 


10.04 


9.58 


7.60 


50.84 


Laredo, Texas 2 


9.25 


10.17 


11.10 


12.91 


12.22 


8.76 


64.41 


Provo, Utah 1 


4.18 


5.86 


7.20 


6.81 


6.32 


4.34 


34.71 


WaUa WaUa, Wash. 3 


4.46 


6.48 


7.10 


8.23 


7.62 


4.37 


38.26 



196. Evaporation and rainfall. — At the Desert Labora- 
tory in Arizona, the evaporation is 9.3 times the rainfall, 
while in most sections of the arid West, the evaporation from 
a water-surface is greater than the rainfall. Evaporation 
determines the efficiency of rainfall in a great measure, par- 
ticularly when the annual rainfall is below 25 or 30 inches. 
A district of rather heavy rainfall, but with high evaporation, 
may not be any better for crops than one with much less 
rainfall if the evaporation is low. 

197. Rainfall efficiency. — A rainfall of 21 inches in the 
Texas Panhandle is no better for crops than 15 inches in the 
upper Great Plains because the evaporation in Texas is nearly 
double that in North Dakota. The line of 20-inch annual 



88 AGRICULTURAL METEOROLOGY 

rainfall passes through the Red River Valley of the North, 
where it is ample for the large grain crops in most years, while 
in Texas it passes through a region that is necessarily devoted 
to grazing or to drought-resistant crops. The seasonal dis- 
tribution of rain is an important factor also in these two dis- 
tricts. 

198. Evaporation from the soil. — ^The rate of evaporation 
from a wet soil surface is about the same as from the surface 
of water in a tank. The evaporation from the surface of the 
soil with the water level maintained 6 inches below the sur- 
face was found in Wyoming to be 95 per cent of that from a 
water surface; with the water level at 12 inches, 70 per cent; 
18 inches, 45 per cent; at 22 inches, 35 per cent. By stirring 
the ground once a week to the depth of 2 inches, the evap- 
oration was retarded about 19 per cent when the water level 
was 22 inches below the surface; when the stirred surface was 
4 inches deep it was retarded 23 per cent; and when 6 inches 
deep, 45 per cent. 

199. Water requirement of plants. — It is not often that 
a crop has during its entire life just the quantity of water that 
best serves its needs, although there is no such thing as a def- 
inite water requirement which is constant for any one kind 
of plant. A plant requires different amounts at separate pe- 
riods of growth and under varying conditions of temperature, 
wind, and sunshine. Investigators have disagreed on the 
water requirement, due in a large degree to different environ- 
ment and methods of operation. 

Plants require several hundred pounds of water in order to 
make a growth of one pound. This means that each day a 
growing plant such as wheat and corn requires several times 
its own weight of water. Water enters the root-hairs and 
passes up the stem to the leaves where it is evaporated, or 
transpired through little openings called stomata. If for any 
reason water cannot be supplied from the soil through the 
roots, the water in the plant evaporates until the plant be- 
comes so dry it dies. 

200. Water requirement at different periods of growth. — 
The grain crops require less water in the early part of the 
growth than during the period when the heads and kernels 
are forming. In a ten-day period of maximum transpiration, 
the annual crops lose about one-fourth of the water lost dur- 



CLIMATE AND CROPS 



89 



ing the season. The transpiration of annual crops rises to a 
maximum a httle beyond the middle of the growth period 
and then decreases until harvest. 

201. Relative water requirements of plants.— Briggs and 
bhantz carried out extensive experiments on the relative 
water requirements of plants at Akron, Colorado, the results 
of which are given m the following table. The figures show 
the ratio of the weight of water absorbed by the plants during 
growth to the weight of dry matter produced, exclusive of 
the roots. 

PRECIPITATION 

Table 6.— Summary of Water-requirement Determinations at 
Akron, Colorado, in 1911, 1912, and 1913, Based on Produc- 
tion OP Dry Matter 







Number Water requirement 






of obser 


- 










vations 


Of species 


Mean of 


Plant 


Botanical 
name 


Years 


or I 


mriely 


J 
genus 


Grain Crops 












Proso: 












Voronezh, C. I. 16 


Panicum mil- 
iaceum 


1 


268 


± 1 




Tambov, S. D. 366 


t( 


1 


270 


± 1 


SQ*? 


Black Voronezh, 


Cf 


1 


341 


±10 


UilO 


S. D. 334 


t( 










Millet: 












Kursk, S. P. I. 


Chaetochloa 


1 


261 


±15 




30029 


italica 










Kursk, S. P. I. 


<( 


2 


265 


± 3 




34771 












Kursk, S. P. I. 


(t 


1 


287 


± 2 


310 


22420 












German, S. P. I. 


IC 


2 


293 


± 9 




26845 












Turkestan, 


tt 


1 


444 


± 9 




S. P. I. 20694 












Sorghum: 












Kafir, Dwarf 


Holcus 


1 


285 


=t= 3 




BlackhuU, C. I. 


(Andropogon) 










340 


Sorghum 











90 



AGRICULTURAL METEOROLOGY 



Table 6. — Summary of Water-requirement Determinations at 
Akron, Colorado, in 1911, 1912, and 1913, Based on Produc- 
tion OF Dry Matter — Continued. 







Number 


Water requirement 






of obser- 














vations 


Of species 


Mean of 


Plant 


Botanical 




or variety 


genus 




name 


Years 










Grain Crops 














Sorghum : — Continued 














Kaoliang, Brown, 


Holcus 


2 


296 


± 


2 




S. P. I. 24993 


Sorghum 












Kafir, White, 


<< 


1 


297 


± 


4 




C. I. 370 














Red Amber, 


(( 


3 


301 


± 


2 




S. P. I. 17563 














Kafir, Early Black- 


(t 


1 


302 


=b 


13 




hull, C. I. 472 














Minnesota Amber, 


(I 


2 


305 


=t 


2 




A. D. I. 341-13 












322 


Kafir, Blackhull, 


« 


2 


308 


± 


4 




S. P. I. 24975 














Mile, White, C. I. 


it 


1 


317 


zir. 


3 




365 














Kafir X Durra, 


{( 


1 


321 


± 


5 




C. I. 198-15-3 














Feterita, C. I. 182 


u 


1 


323 


± 


4 




Milo, S. P. I. 24960 


ii 


1 


324 


=b 


4 




Durra, White, 


i( 


1 


327 


± 


2 




S. P. I. 24997 














Milo, Dwarf, 


C( 


2 


344 


± 


3 




S. P. I. 24970 














Sudan Grass, 


tt 


1 


467 


± 


9 




S. P. I. 25071 














Corn: 














Esperanza 


Zea Mays 


2 


315 


=fc 


3 




X Esperanza 


ii 


1 


325 


=fc 


2 




Indian Flint 


ii 


1 


342 


=fc 


5 




China White X Hopi 


a 


1 


345 


± 


3 




Hopi 


a 


2 


361 


dtz 


6 


368 


China White X Laguna 


a 


1 


376 


± 


5 




Northwestern Dent 


ii 


3 


377 


± 


7 




Laguna 


a 


1 


384 


± 


8 




Bloody Butcher 


ii 


1 


405 


=t: 


7 





CLIMATE AND CROPS 



91 



Table 6. — Summary of Water-requirement Determinations at 
Akron, Colorado, in 1911, 1912, and 1913, Based on Produc- 
tion OP Dry Matter — Continued 







Number 


Water requirement 






of obser- 














vations 


Of species 


Mean of 


Plant 


Botanical 




or variety 


genus 




name 


Years 










Grain Crops 














Corn : — Continued 














Iowa Silvermine 


Zea Mays 


2 


407 


=fc 


5 




China White 


u 


2 


413 


=t 


5 




Wheat: 














Turkey, C. I. 1671 


Triticum 
SBstivum 


1 


473 


=t: 


8 ^ 




Kharkov, C. I. 1583 


(I 


1 


475 


± 


8 




Kubanka, C. I. 


Triticum- 


3 


492 


± 


4 




1440 


durum 












Galgalos, C. I. 


Triticum 


1 


496 


± 


4 


, 513 


2398 


sestivum 












Emmer, C. I. 2951 


Triticum 
dicoccum 


2 


545 


d= 


7 




Spring Ghirka, 


Triticum 


2 


550 


db 


3 




C. I. 1517 


sestivum 












Marvel Bluestem, 


a 


2 


559 


± 


4 




C. I. 3082 














Barley: 














Hannchen, C. I. 


Hordeum 


2 


502 


=t 


4 




531 


distichon 












Beardless, C. I. 716 


Hordeum 
vulgare 


2 


534 


± 


7 


534 


Beldi, C. I. 190 


<( 


2 


542 


± 


3 




White Hullless, 


it 


2 


556 


± 


2 




C. I. 595 














Buckwheat: 


Fagopyrura 
esculentum 


1 


578 


± 


13 


578 


Oats: 














Canadian, C. I. 444 


Avena sativa 


2 


559 


=fc 


8 ^ 




Swedish select, 


(< 


3 


594 


± 


4 




C. I. 134 












597 


Burt, C. I. 293 


(( 


3 


613 


=1= 


3 
9 _ 




Sixty-day, C. I. 165 


« 


2 


622 


rt 





92 



AGRICULTURAL METEOROLOGY 



Table 6. — Summary of Water-requirement Determinations at 
Akron, Colorado, in 1911, 1912, and 1913, Based on Produc- 
tion OF Dry Matter — Continued 





' 


Number 


Water requirement 






of obser- 












vations 


Of species 


Mean of 


Plant 


Botanical 




or variety 


genus 




name 


Years 








Grain Crops 












Rye, spring, C. I. 73 


Sccale cereale 


2 


685 


± 7 


685 


Rice, Honduras, C. I. 


Oryza sativa 


2 


710 


=^15 


710 


1643 












Flax, North Dakota, 


Linum usitat- 


1 


905 


=±=25 


905 


No. 155 


issimum 










Other crops 












Beet, sugar: 












Morrison-grown 


Beta vulgaris 


2 


397 


^ 6 


397 


Kleinwanzleben 


'• 










Potato: 












Irish Cobbler 


Solanum tu- 
berosum 


2 


554 


± 9 


636 


McCormick 


(( 


1 


717 


±11 




Cotton, Triumph 


Gossypium 
hirsutum 


2 


646 


±11 


646 


Legumes: 












Alfalfa, Peruvian 


Medicago 


1 


651 


±12 




S. P. I, 30203 


sativa 










Alfalfa, Grimm, 


(C 


2 


844 


± 8 




A. D. I. E23-20-52 










831 


Alfalfa, yellow- 


Medicago 


1 


865 


±18 




flowered 


falcata 










Alfalfa, Grimm, 


Medicago 


2 


983 


± 9 




S. P. I. 25695 


sativa 











This table shows that the grain crops can be grouped into 
two sections. Those of low water requirements are proso, 
millet, sorghum, and corn, and those of high water require- 
ments are wheat, barley, oats, rye, and flax. 

Those crops of low water requirement are the late maturing 
ones which make their best growth during the hottest and 
driest portion of the summer, while those of high water re- 



CLIMATE AND CROPS 93 

quirement mature during midsummer and make their best 
growth in the earlier, cooler part of the year. 

Representing the water requirement of proso as 1, the water 
requirement of the grain crops is as follows: Millet, 1.06; sor- 
ghum, 1.10; corn, 1.26; wheat, 1.76; barley, 1.83; buckwheat, 
1.98; oats, 2.04; rye, 2.34; rice, 2.42; and flax, 3.38. In other 
words, flax requires more than three times as much water 
and rice more than twice as much water as proso and millet 
in producing a pound of dry matter. 

Representing the water requirement of the sugar-beet as 1, 
the values for the "other crops," exclusive of the legumes 
are as follows: Cabbage, 1.36; Irish Cobbler potato, 1.39 
watermelon, 1.51; cantaloupe, 1.57; turnip, 1.60; cotton, 1.63 
cucumber, 1.80; wheat-grass, 1.85; rape, 1.87; squash, 1.89 
pumpkin, 2.10; and brome-grass, 2.56. 

202. Farming in the semi-arid regions. — It is customary 
to give the greatest attention to the total annual rainfall in 
considering the desirability of a region for dry-farming, al- 
though the amount of rain that falls during the growing sea- 
son and the character of the fall is of equal importance. The 
amount that may be lost by run-off with heavy local showers, 
the evaporation, altitude, length of the growing season, the 
wind, and the like, must all be carefully considered. 

203. Irrigation in humid districts. — There is often a se- 
rious lack of moisture in humid regions, where because of the 
greater apparent requirements of the adapted plants, a 
drought of equal intensity may cause greater damage than 
in drier districts. Even in a region like Florida where the 
rainfall can be classed as heavy, both for the year and for the 
growing season, there are periods when practically all crops 
Vv^ould be benefited by irrigation. 

SUNSHINE OR LIGHT 

Next to moisture, light is the most important external 
factor affecting the form of plants, as it plays an important 
part in controlling the plant structure. 

204. Clouds. — Sunshine is usually considered under the 
head of moisture in the atmosphere as shown by the cloudi- 
ness, yet a careful consideration of the effect of sunshine will 
show that this is a separate climatic factor of very great im- 
portance. 



94 AGRICULTURAL METEOROLOGY 

205. Solar energy. — In some places where the rainfall is 
sufficient but the temperature is too low for the best growth 
of plants, as in Alaska, sunshine becomes the most important 
climatic factor. In fact sunshine and heat can hardly be 
separated. Solar energy is the factor that enables the plants 
to make use of the food brought to the roots by soil-moisture 
and carried to the leaves by transpiration, whether this en- 
ergy is called ^'degrees'' or "calories." 

206. Sunshine-hour degree. — A value called the "sun- 
shine-hour degree" has been obtained by multiplying the 
average daily heat necessary to grow and mature a crop, by 
the total possible hours of sunshine from planting to har- 
vesting. In the eastern part of the United States, the sun- 
shine-hour degree for corn is 80,313 between latitudes 30 and 
35 degrees; 65,778 between latitudes 35 and 40, and only 
47,887 between latitudes 40 and 45 degrees. This shows that 
the sunshine-hour degrees necessary to make a crop diminish 
as the latitude increases, and explains to a partial extent at 
least why there is a decided difference in the quantity of heat 
necessary to grow and mature the same crop at various lati- 
tudes because of the difference in the number of hours of day- 
light. It must be noted, however, that the varieties and 
even the types of corn grown in different latitudes account 
for part of this difference. 

207. Variation with latitude. — From the pole to the 
equator, the luminous intensity of the sunlight increases by 
ten, but its duration during the growing season is twice as 
great at the poles as at the equator. The varying number of 
possible hours of sunshine, or hours of daylight, at different 
seasons of the year, for various latitudes is shown in the fol- 
lowing table: 

Table 7. — Total Number of Hours op Sunshine Possible at 

Season 

June 11 to 20 
Dec. 11 to 20 



June 11 to 20 
Dec. 11 to 20 



Different Latitudes 










Latitude 






24 


26 


28 


30 


32 


135.7 


137.2 


139.7 


140.3 


141.9 


106.2 


104.8 


103.3 


101.7 


100.1 


34 


36 


38 


40 


42 


144.7 


145.5 


147.5 


149.5 


152.7 


98.4 


96.7 


94.8 


92.9 


90.7 



CLIMATE AND CROPS 95 

Table 7. — Total Number op Hours op Sunshine Possible at 
Different Latitudes — Continued 
Season Latitude 





44 


46 


48 


50 


June 11 to 20 


154.1 


156.7 


159.6 


162.8 


Dec. 11 to 20 


88.4 


85.9 


83.2 


80.2 



The increased production of pigments in flowers and fruits, 
as well as the ethereal oils, at higher latitudes is probably 
correctly attributed to the increased hours of sunshine during 
plant development. 

208. The effect of Ught.— The action of light on plants 
may be invigorating or retarding, beneficial or detrimental, 
depending on its intensity and the precise physiological func- 
tion involved. The unequal intensity of illumination in the 
different latitudes, and the increasing duration of the hours 
of sunlight from the equator to the poles, do not fail to stamp 
their mark on the vegetation. 

209. Different intensities. — It is nowhere too dark or too 
light for plants to grow. The growth of length of stem and 
roots is at an optimum when light is totally excluded. The 
formation of chlorophyll and that of some of the pigments 
is at a maximum under light of moderate intensity. The min- 
imum of light required for the reduction of carbon dioxide is 
considerably higher than that for the manufacture of color- 
ing matter. 

210. The effect of sunshine.— The effect of direct sun- 
shine naay be beneficial or detrimental to plant development, 
depending on other conditions, although few quantitative 
records have been made of its effects. Other things being 
equal, an increased amount of sunshine means a larger quan- 
tity of plant substances, especially sugar and starches. 

211. Sunshine raises the temperature. — The tempera- 
ture of objects in direct sunshine is higher than that of the 
surrounding air due to the absorption of the radiant energy. 
The effect on the ground is favorable in the spring as the soil 
is warmed more rapidly and is more favorable for germination 
and growth. During weather too cool for normal growth, 
direct sunshine promotes the activity of plants. 

212. Sunshine sometimes unfavorable. — The soil some- 
times becomes so highly heated in hot summer weather, how- 



96 AGRICULTURAL METEOROLOGY 

ever, that shallow roots are injured. Peas, beans, tomatoes, 
squash, melons, and strawberries are sometimes damaged in 
this way. Fruit-buds may be advanced too rapidly under 
warm sunshine, and frequently maturing fruit such as apples, 
oranges, and lemons are sunburned and damaged by direct 
sunshine. Sun-scald often occurs also by the direct effect of 
strong sunshine on the south sides of the bole and large limbs 
of fruit-trees in winter. Evaporation goes on rapidly; the 
temperature is raised to a high point under the solar energy 
and then falls rapidly after the sun goes down. The tissue 
next to the wood is thus killed and the bark peels off. 

Bright sunshine raises the temperature of plants and thus 
promotes transpiration. It may injure the pollen if the 
weather is too hot, but generally bright sunshine favors in- 
sect activity and thus aids in pollination. 

213. Sunshine for tomato pollen.— Experiments in Wis- 
consin showed that the percentage of germination and rate 
of growth of tomato pollen are favored by sunshine, as indi- 
cated by the following: 



Temper- 
ature 
Deg. C. 


Average percentage 

of germination 

Sunshine Cloudy 


Rate of growth in 

mm. per hour 

Sunshine Cloudy 


33 


66 41 


45 27 


34 


64 42 


43 28 


36 


68 46 


49 32 



214. Diffuse light. — A certain amount of light is required 
by all of the higher forms of plants for the proper develop- 
ment of leaves, flowers, and fruit. Strong light aids in the de- 
composition of carbon and the elimination of water-vapor in 
plants. 

215. Lack of knowledge. — Our knowledge of the relation 
of light to plant life is comparatively slight. It is known that, 
other things being equal, the longer the hours of daylight the 
higher the sugar-content in sugar-beets. It is also known 
that light has some effect on the coloring of and probably the 
texture of fruit, and that the coloring of some flowers is 
brighter in higher latitudes, due partly, it is thought, to in- 
creasing hours of daylight. 

216. Knowledge of sunshine e^ect important. — Some 
experiments made in England shov/ that sunshine at just the 



CLIMATE AND CROPS 97 

right time produced some extraordinary results. For ex- 
ample, if the yellow tomato received plenty of sunshine at the 
proper time the effect on the yield of fruit was marvelous, 
whereas if it had a sunless period at a certain quite unex- 
pected hour a very poor yield resulted. The critical sunshine 
period for the red variety was not at all the same as for the 
yellow. 

217. American Beauty rose. — It is now known that the 
setting of buds of the American Beauty rose is largely de- 
termined by the amount of light supplied. During extended 
periods of cloudy and dull weather in the winter season, the 
supply of these flowers is frequently less than the demand. 

218. Sunshine, temperature, and moisture. — On the 
Cahfornia coast near Carmel, there is a region exceptionally 
well fitted for growth of beans. On days having a tempera- 
ture not higher than 70° there is usually no sunshine. Ocean 
fog-banks extend only a short distance inland. These days 
constitute about 70 per cent of the whole time from July 3 to 
September 10. In this period in 1916, the sunshine was 
only 9 per cent of the possible. Humidity is rather high; at 
night the temperature is rather low. This climate is ideal for 
many plants as the luxuriant growth of geraniums, fuchsias 
and foxgloves shows. It is such cool and humid conditions 
that make possible along the California coastal belt the grow- 
ing of beans and many other vegetables to remarkable per- 
fection. 

WIND 

Wind is an important climatic element and the factors con- 
sidered are its velocity or total movement, prevailing direc- 
tion, and the character of the country from which the wind 
blows. 

219. Beneficial winds. — Wind aids in drying the soil in 
the spring and the chinook wind clears the snow from the 
ranges in some northwestern sections, allowing for winter graz- 
ing. It equalizes the temperature on the leeward sides of 
large bodies of water and sometimes prevents frost damage 
on clear nights. 

220. Damaging winds. — The wind dwarfs trees, damages 
young grain or other crops in dry regions by blowing the soil, 
blows off fruit, scatters the seeds of some weeds, and increases 



98 AGRICULTURAL METEOROLOGY 

evaporation and transpiration. In the central Great Plains 
region, young grain plants maybe blown out, covered, or cut 
off by blowing sand. Strong winds may blow or strip blos- 
soms from the trees or prevent insects from working among 
the blossoms. Long continued warm dry wind injures blos- 
soms by evaporating the secretion from the stigmas thereby 
preventing the retention and germination of pollen. Damp 
warm winds, if long continued, are also unfavorable to polli- 
nation and fertilization. A cold dry wind at the time of the 
blooming of fruit seems to chill vegetation and stops the nor- 
mal functions, not only of blossoms but of leaves. Winds 
distribute plant disease germs. 

LABORATORY EXERCISES 

1. Paragraph 142. Record the temperature of the soil at one inch 
depth and the temperature of a water surface in bright sunshine. Ob- 
tain similar data on a clear still night. 

2. Paragraph 157. Determine the "zero" of vital temperature for 
various seedlings. 

3. Paragraph 160. Obtain temperature and crop planting and har- 
vesting data and calculate the total effective heat sums for several 
places by the different methods. 

4. Paragraph 163. It may be possible for two or more students to 
work out some growth observations as developed by Lehenbauer. 

5. Paragraph 166. Take a series of plant temperature observations. 

6. Paragraph 175. Calculate Lissner's aliquot for some plant for 
different latitudes. 

7. Paragraph 181. Make some records of soil temperature. Dr. 
Forrest Shreve, Tucson, Arizona, Secretary Ecological Society of Amer- 
ica, is attempting to standardize soil temperature records. Consult him. 

8. Paragraph 184. Take some soil temperature observations under 
different soil coverings. 

9. Paragraph 185. Make some temperature observations at the sur- 
face of the ground under different thicknesses of snow covering. Com- 
pare these with simultaneous observations of air temperature. 

10. Paragraph 193. More "wilting coefficient" observations are 
needed and where the necessary apparatus are available records should 
be made. 

11. Paragraph 194. More transpiration records are needed. Consult 
the plant physiologist as to methods. 

12. Paragraph 198. More records are needed of evaporation from 
the soil as compared with a free water surface. Consult the agronomist. 

13. Paragraph 203. Tests should be made of the value of a sufficient 
water supply during periods of drought, in every state in the central and 



CLIMATE AND CROPS 99 

eastern parts of the country. Arrangements can readily be made to irri- 
gate small plats as needed. Careful records must be kept of all mete- 
orological factors, water applied and growth results, as compared with 
those receiving natural rainfall. 

14. Paragraph 206. Calculate sunshine-hour degree values for dif- 
ferent latitudes. 

15. Paragraph 208. Records of the action of direct and diffuse sun- 
light at different stages of plant growth, not only in summer, but in 
greenhouses in winter, are easily made and greatly needed. 

In the Journal of Agricultural Research for March 1, 1920, Garner and 
Allard have given the results of some very valuable studies on the 
effect of differences in the length of the daylight period on plants. The 
following are among the important facts determined: 

(1) The relative length of the day is a factor of the first importance in 
the growth and development of plants, particularly with respect to 
sexual reproduction. 

(2) In a number of species studied it has been found that normally 
the plant can attain the flowering and fruiting stages only when the 
length of day falls within certain limits, and, consequently, these 
stages of development ordinarily are reached only during certain seasons 
of the year. 

(3) The relationships existing between annuals, biennials, and 
perennials, as such, are dependent in large measure on responses to the 
prevailing seasonal range in length of day. 

(4) The seasonal range in the length of the day is an important factor 
in the natural distribution of plants. 

REFERENCES 

Climate. R. DeC. Ward. G. P. Putnam's Sons (2nd Edition), 1918. 

Growth of Maize Seedlings in Relation to Temperature, P. A. Lehen- 
bauer. Physiological Researches No. 1, December, 1914. 

Measuring the Temperature of Leaves. Edith B. Shreve, The Scien- 
tific American, Vol. CXX, No. 15, April, 1919. 

Physiological Temperature Indices for Study of Plant Growth in Re- 
lation to Climatic Conditions. B. E. Livingston, Physiological Re- 
searches No. 8, Johns Hopkins University. 

Temperature. Raphael Zon, Monthly Weather Review, 1914, p. 217. 

Relation between Temperature and Crops. D. A. Seeley, Monthly 
Weather Review, July, 1917. 

Relation of Temperature to Planting and Harvesting Dates. J. B. 
Kincer, Monthly Weather Review, Aj^ril, 1919. 

The Temperature of the Soil and the Surface of the Ground. D. A. 
Seeley, Monthly Weather Review, November, 1901. 

Heat Transference of Soils, Bureau of Soils, Bulletin 59. 

Missouri Agricultural Experiments Station Research Bulletin No. 4. 



100 AGRICULTURAL METEOROLOGY 

Sixteenth Annual Report Nebraska Experiment Station. 

Soil Temperature, Michigan Agricultural Experiment Station, Techni- 
cal BuUetin No. 26. 

A Single Index to Represent both Moisture and Temperature Condition 
as Related to Plants. B. E. Livingston, Physiological Researches, 
Vol. I, No. 9, May, 1916. 

Daily Transpiration During the Normal Growth Period and its Corre- 
lation with the Weather, Journal of Agricultural Research, Octo- 
ber, 23, 1916. 

Dry Farming in Relation to Rainfall and Evaporation, Bureau of Plant 
Industry Bulletin 1S8. 

Evaporation from Irrigated Soils, Office of Experiment Stations, Bul- 
letin 248. 

Evaporation, Wyoming Experiment Station Bulletin No. 52. 

Factors Influencing the Water Requirements of Plants, Washington 
Agricultural Experiment Station Bulletin 146. 

Rainfall as a Determinant of Soil Moisture, Shreve, Plant World, Jan., 
1914. 

Relative Water Requirement of Plants, Journal of Agricultural Re- 
search, Vol. Ill, No. I. 

Transpiration as a factor in Crop Production, Nebraska Experiment 
Station Research Bulletin No. o. 

Water Requirements of Plants, The. Briggs and Shantz, Bureau of 
Plant Industry Bulletin Nos. 284 and 285. 

Wilting Coefficient for Different Plants, Bureau of Plant Industry 
Bulletin No. 230. 

Effect of the Relative Length of Day and Night and Other Factors of 
the Environment on Growth and Reproduction in Plants. W. W. 
Garner and H. A. Allard. Journal of Agricultural Research, 
Vol. XVIII, No. 11. 



CHAPTER VI 

CLIMATE AND FARM OPERATIONS 

Clknate is the most fundamental of all the factors which 
determine crop distribution and hence farming methods. 

221. Well-defined crop zones. — East of the Rockies the 
agricultural provinces have more or less definite climatic 
boundaries, extending in a general way in an east-west direc- 
tion, conforming to the isothermal trend. In these regions 
there are five more or less distinct provinces, as follows: (1) 
the southern subtropical coast; (2) the cotton-belt; (3) the 
corn and winter wheat belt; (4) the spring wheat belt, and 
(5) the hay and pasture region. 

222. The southern subtropical coast has a warm and 
comparatively equable climate, with an average winter tem- 
perature ranging from about 55° along the central Gulf coast 
to 70° in extreme southern Florida, and an average summer 
temperature of 80° to 82°. The principal crops in this prov- 
ince are winter truck, citrus fruits, sugar-cane, and rice. 

223. The cotton-belt. — Most of the cotton-belt has an 
average winter temperature of 45° to 55° and an average sum- 
mer temperature ranging from about 78° at the northern 
boundary to 81° at the southern. The frostless season along 
the northern border averages about 200 days in length. Cot- 
ton forms about 47 per cent of the acreage and 61 per cent 
of the value of all crops grown in this belt. 

224. Com and winter wheat belt. — The average winter 
temperatures of the corn and winter wheat belt range from 
40° in the southern part to about 15° in southern Minnesota. 
The average summer temperatures range from about 70° in 
the northern part to 78° in the southern. The average frostless 
season ranges from 140 days at the north to about 200 at the 
south. This is a region of diversified farming, but corn usually 
contributes nearly 45 per cent and wheat nearly 15 per cent to 
the acreage of all crops. 

101 



102 AGRICULTURAL METEOROLOGY 

225. The spring wheat belt lies mostly in the north- 
central section of the country, principally in the states of 
Minnesota, the Dakotas, and Montana. The average sum- 
mer temperature along the Canadian boundary is about 65°, 
while the southern boundary of the belt conforms approxi- 
mately to the mean summer isotherm of 70°. On the average, 
the frostless season varies from 100 days in the north to about 
140 days in the south. Farming is rather diversified in this 
section also, but spring wheat forms 36 per cent of the crop 
acreage. 

226. The hay and pasture region is less well defined than 
the others mentioned, and is, as a rule, a region of diverse 
agricultural conditions. It includes mostly the northern bor- 
der states from Minnesota eastward, extending into the Mid- 
dle Atlantic states and Appalachian Mountain districts. The 
average smnmer temperatures range from about 62° to 70° 
and the average winter temperatures from 10° to 25°. The 
dairy products in this region amount to more than one-half 
of the total for the United States. 

227. The shifting of crop areas. — In a comparatively new 
country where transportation facilities are not well estab- 
lished, certain varieties of crops will be grown which, it will 
later be found, can be raised more economically elsewhere be- 
cause of a more favorable climate, and the ground devoted 
to some better paying crop. 

228. A change in farm operations. — There is sometimes 
an unconscious shifting of farm activities that may not be 
noticed for several years and then can be explained only by 
the influence of climate. 

229. Butter- and cheese-making in Wisconsin. — At one 
time both butter and cheese factories were scattered over cen- 
tral and southern Wisconsin. Now, however, the commer- 
cial cheese factories are grouped into well-defined areas in the 
central and northern parts while the butter industry princi- 
pally occupies southeastern Wisconsin. 

By comparing the distribution of these two industries with 
climatic maps, it develops that the commercial cheese fac- 
tories are almost exclusively within areas where the potential 
growing season is less than 150 days in length, while the com- 
mercial butter factories are where the season is over 150 days. 
It develops also that there are no cheese factories south of 



CLIMATE AND FARM OPERATIONS 103 

the mean summer isotherm of 70°, and that the mean iso- 
therm of 65° for the cheese-making season approximately 
hmits the cheese-producing regions in Wisconsin on the south. 

230. Length of the growing season. — In all farm opera- 
tions it is important to know the length of the average grow- 
ing season, and the length of time from planting to maturity 
of the various crops. In Ohio, for example, the average time 
from planting to harvesting early potatoes is from 80 to 100 
days, and for late potatoes 120 to 130 days. The average pe- 
riod between the last killing frost in the spring and the first 
in the autumn is from less than 150 to slightly over 170 days. 
It is clear, therefore, that while either early or late potatoes 
can be raised in Ohio, it is not possible to raise two crops on 
the same land. Farther south, however, where the length of 
the growing season is over 200 days, two crops may be suc- 
cessfully grown that do not require over 100 days to mature. 

231. Climate and the number of crops. — Variations in the 
rainfall, temperature, and length of growing season make 
what have been termed the " no-crop climate," the " one-crop 
chmate," the " two-crop chmate," and the " continuous crop 
cUmate." Many so-called " worn-out " farms have been re- 
claimed by using the cropping system adapted to the climate. 

232. The double-cropping system. — In the southeastern 
states there are two fairly well-defined wet seasons, one in 
winter and one in summer, separated by short drier seasons 
in spring and fall. Moreover, during the winter the tempera- 
ture is high enough to keep the more hardy crops, such as 
grains, grass and winter legumes, growing. This region is, 
therefore, well adapted for a double-crop system, as distin- 
guished from the Northwest, where the winters are too cold 
for growth and where there is only one wet season. 

233. The distribution of rain. — It is important to know 
the seasonal distribution of rainfall as well as the annual 
amount, in considering available crops and farm methods. 
It would be very unwise, for example, to plant a crop that re- 
quires a good deal of moisture just before a normal dry sea- 
son, or if a crop needs dry weather at certain periods of growth 
to seed it so that this critical period would come at a time 
that usually brings heavy rains. 

234. Rain and harvesting dates. — There are sections 
where alfalfa can be grown very successfully, but where the 



104 AGRICULTURAL METEOROLOGY 

frequency of rainfall during the summer months makes it al- 
most impossible to cure it. There are other districts where 
the value of hay is less than that grown in other sections of 
the same state even, because frequent rains occur in one re- 
gion during the harvesting period while it is comparatively 
dry in the other. 

235. Arid and semi-arid regions. — More than one-half 
of the land area of the globe receives an annual rainfall of 
less than 20 inches. The large areas of arid or semi-arid 
lands in the western part of the United States make it 
necessary to practice irrigation or dry-farming methods 
for successful agriculture, both well-defined climatic types 
of farming. 

236. Larger farms necessary in drier regions. — It has 
been pointed out that on some of the table-lands in western 
Nebraska where the rainfall is less than 20 inches, it takes 
about one and one-half sections of land to produce an amount 
of plant-food equal in value to that produced on one-quarter 
section of upland in the southeastern part of the state where 
the rainfall is 30 inches or more, the mean annual tempera- 
ture is higher, and the length of the growing season is con- 
siderably longer. 

237. Weather risk. — In order to be entirely successful in 
farm operation, a man must know and take account of the 
degree of risk that he runs from climatic conditions in raising 
any crop. He must calculate the risk of loss by rains and low 
temperature ; the average length and intensity of drought pe- 
riods; the probability of hail and wind damage, and the dan- 
ger of frost in the spring and fall. 

238. Spring frosts. — In raising any crop, for example, the 
value of which is determined by the earliness with which it 
can be put on the market, the grower must consider whether 
the price anticipated will make it wise for him to plant at such 
a date as to make the risk of loss by frost 75 per cent or 50 
per cent or whether he should make the risk only 10 per cent 
or less. 

The same considerations should be given to the probablity 
of fall frost damage, probability of loss by hail, and the like. 
The climatological publications of the Weather Bureau give 
very complete and definite information about all these 
matters. 



CLIMATE AND FARM OPERATIONS 105 

LABORATORY EXERCISES 

1. Paragraph 221. Chart crop zones in connection with tempera- 
ture, sunshine, and rainfall maps. 

2. Paragraph 229. Local inquiry may show other examples of the 
shifting of crop areas or of farm activities. 

3. Paragraph 230. Determine the possible growing season locally 
(see frost maps) and determine what two crops can be grown on the 
same land. 

4. Paragraph 231. What is the local climate? What sections of the 
United States have a "continuous-crop" climate? Are there any sec- 
tions of the United States with a "no-crop" climate? 

5. Paragraph 233. Obtain monthly rainfall data from the State sec- 
tion Director and chart the seasonal distribution. Are there any local 
crops that should be planted at a different date? 

6. Paragraph 237. Calculate some of the weather risks in your 
state or locality. 

REFERENCES 

A Preliminary Study of Climatic Conditions in Maryland as Related 
to Plant Growth. F. T. McLean. Maryland Weather Service; 
Vol. IV, Part la, 1917. 

Climatic Factors in Relation to Farm Management Practice. J. Warren 
Smith, American Fami Management Association, November, 1916. 

CUmate of Wisconsin and its Relation to Agriculture. Whitson and 
Baker, Wisconsin Experiment Station, Bulletin 223, 1912. 

Climate of Michigan and its Relation to Agriculture. D. A. Seeley, 
Michigan State Board of Agriculture, 1917. 

Experiment Station Bulletin No. 87, Knoxville, Tennessee. 

Effect of Climate and Soil upon Agriculture. R. R. Spafford, Uni- 
versity Studies, Lincoln, Nebraska, 1916. 

Relation of Meteorological Study to more Logical Systems of Crop- 
ping and to Crop Production. J. F. Voorhees, Proceedings of the 
Society for the Promotion of Agricultural Science, 1912. 

Relation of Temperature and Rainfall to Crop Systems and Produc- 
tion. J. F. Voorhees, Agricultural Experiment Station Bulletin 
No. 91, Knoxville, Tennessee, 1911. 

Relation of the Weather Service to the Farmers of Tennessee. J. F. 
Voorhees, Agricultural Experiment Station Bulletin No. 87, Knox- 
ville, Tennessee, 1910. 

Weather as a Business Risk in Farming. Reed and Tollcy, Geograph- 
ical Review, Vol. II, No. I. 

A Graphic Summaiy of American Agriculture. Middleton Smith and 
others. Yearbook, U. S. Department of Agriculture, 1915, j). 329. 

A Graphic Summary of Seasonal Work on Farm Crops. O. E. Baker 
and others, Yearbook, U. S. Department of Agriculture, 1917, p. 537. 



CHAPTER VII 
WEATHER AND CROPS 

Plant growth is the result of so many different factors, and 
these influences have such complex combinations that it nat- 
urally has been deemed difficult if not impossible to deter- 
mine the relation to, or influence of, any one of these factors 
in varying the yield of a crop. 

While it may never be possible to determine the exact in- 
fluence of any particular weather factor at any specified pe- 
riod of growth, it is believed to be entirely feasible to learn 
which weather element has the greatest influence in varying 
the yield or what coml)ination of weather factors are most 
favorable or unfavorable at certain periods of growth. By the 
three methods mentioned under paragraph 101 it is thought 
possible to find the most critical period in the development of 
a crop and then to determine the factor that has the greatest 
influence in varying the yield. 

239. Weather variation effects relative. — As there are 
wide variations in climate within the limits of the United 
States, not only in mean temperature and annual rainfall, but 
in sunshine, temperature extremes and rainfall distribution, it 
follows that the critical period of growth of a crop plant will 
vary in sections of the country and the combination of 
weather factors will be different and affect crops differently. 
In other words, the study of the critical period of growth and 
of the weather factor producing the greatest influence on the 
yield must l)e for definite climatic districts. 

240. Warm and. cold season crops. — The field, orchard, 
and garden crops grown in the United States are native to 
various countries, although most of them originated in what 
are now tropical or subtropical regions differing widely in 
climatic condition. As many of these are grown in such dif- 
fering climates, the same crop may be properly called a 
"warm season" crop in one region, and a "cool season" 

106 



WEATHER AND CROPS 107 

crop in another. In general, however, most crops fall into 
well-defined groups of cool or warm, dry or wet season crops. 

The following classifications, therefore, are rather general, 
while the actual studies on the effect of weather on the yield 
of various crops are for the particular districts referred to. 
In all of these studies the wide varietal differences as well as 
the inter-relation of soil and climatic conditions, and the like, 
must not be lost sight of. Such comparatively few systematic 
experiments required to develop accurate information along 
these lines have been made that it is difficult to generalize 
too freely. Undoubtedly some of the prevailing ideas which 
have not been experimentally tested will require modifica- 
tion as the character, extent, and reason for plant reactions 
to environment are better understood. At the same time the 
subject is of such vital importance that it seems desirable to 
give the most available information, with the understanding 
that the whole matter is in need of further study and investi- 
gation. 

241. A complex problem. — The ultimate yield of a given 
plant, or number of representative plants, is the sum total of 
all the influences of environment on it from the time of plant- 
ing to harvesting, including the quality of the seed and the 
condition of the soil at time of planting. The problem be- 
comes one of stating the condition of a plant or crop at a 
given epoch of its growth and combining therewith the re- 
sults of subsequent growth as a function of weather and other 
factors. 

Obviously the weather and other influences exert their ef- 
fects as a function of time, and also it must be recognized 
that the effect due to any given weather depends on the age 
or condition of the crop at the time. The influence of past 
weather conditions as well as the inter-relation of two or more 
weather factors must not be lost sight of. 

All these considerations serve to indicate the complexity 
of the problem and make it plain that in the beginning at 
least one must limit himself very largely to coarse approx- 
imations and to a comparatively small number of relatively 
potent factors. 

It is unfortunate that census data on crop yields in 1909 
must be used, as crop areas have changed very materially in 
some instances since that year. 



108 



AGRICULTURAL METEOROLOGY 



FIBER CROPS 

Under fiber crops will be treated cotton, flax and hemp, and 
the influence of climate on them. 

Cotton 

Cotton is of tropical origin but is now grown in many 
places as far north as 40° North Latitude and south to 
30° South Latitude. It is a perennial shrub in the tropics 
but as it is killed by frost, the seed must be planted annually 
in the temperate districts. 

242. Climatic limits. — The successful cultivation of cot- 
ton has definite climatic boundaries, established primarily 




23 ANNUAL PRECIPITATION 



Fig, 25. — Cotton acreage in the United States in 1909. Each dot 
represents 10,000 acres. 

by temperature, although the amount of rainfall appears also 
to influence the location of the principal producing areas 
within the region where temperatures are favorable. 

243. In the United States. — Fig. 25 shows the distribu- 
tion of cotton-growing in the southeastern part of the United 
States, although since the year 1909 the production of this 
crop has developed considerably in Arizona and California. 
Fully 60 per cent of the world's production of cotton is grown 
in the United States. There are three well-defined areas in 



WEATHER AND CROPS 109 

this region in which cotton is cultivated more extensively 
than in other sections of the belt. One of these extends 
from central and northwest South Carolina through cen- 
tral Georgia into southeastern Alal^ama; another is from 
western Tennessee down the Mississippi Valley to about the 
latitude of southern Arkansas, and a third comprises a belt 
extending in a northeast-southwest direction through central 
Texas at about longitude 97°. 

244. Length of growing season. — Cotton is a slow- 
growing crop and seldom matures in less than 180 days after 










Fig. 26. — ^Average date when cotton planting begins. 

the seed is planted. Very little is grown in the United States 
where there are less than 200 days between the average dates 
of killing frosts. Figs. 26 and 27 respectivel}^ show the dates 
when planting and harvesting are begun in the United States. 
The picking of the late top crop is sometimes not completed 
until late winter. 

245. Temperature and cotton. — Temperature is the prin- 
cipal limiting factor controlling the geographic distribution 
of cotton. It cannot successfully be grown commercially where 
the mean summer temperature is below 77° or 78°. The tem- 
peratures should be high both day and night for best growth. 
Cool nights with warm days cause premature ripening, but 
after the plant has made its vegetative growth cool nights 
are favorable for maturing the bolls and ripening the seed. 

246. Fall frosts damaging. — Cotton, like most other 
warm weather crops, is subject to damage by frost in the fall, 



no 



AGRICULTURAL METEOROLOGY 




WEATHER AND CROPS 111 

especially when the development is slow during the growing 
season as a result of unfavorable weather. There is a rather 
close relation between the temperature during the early pe- 
riod of growth and the lateness or earliness of maturity. 

247. Temperature and the progress of ginning. — The 
relative amount of cotton ginned to a given period during the 
early harvest season gives a good indication of the earliness 
or lateness of the crop and reflects this feature more than it 
gives an idea of the size of the crop. Fig. 28 shows the rela- 
tion of the mean temperature for the months of May and 
June to the amount of cotton ginned to September 25, in the 
states of Georgia and Alabama for the period for 1905 to 1915. 
It shows a very marked influence of the temperature during 
these months on the advancement of the crop to maturity. 

248. Rainfall and cotton. — Cotton needs a moderate but 
regular supply of moisture, hence light frequent showers with 
plenty of sunshine between produce the best condition for 
its growth. An over-supply of moisture causes too rank a 
growth at first, deferring the fruiting and causing a develop- 
ment of vegetative limbs instead of the fruiting branches. 
In the humid regions, too much moisture interferes with the 
development of the plant, either by stunting its growth or by 
causing the shedding of buds and young bolls. Shedding is 
also caused by too little soil-moisture, a content of 15 per cent 
being the critical point on the best cotton soils. 

249. Rainfall distribution important. — The mean annual 
rainfall in the cotton-belt varies from 35 inches in the impor- 
tant cotton area in Texas to 50 inches or more in the central 
and eastern areas, hence has no great effect on the distribu- 
tion of cotton production. Considering the warm season 
rainfall (April to September), however, it is found that the 
Texas belt averages about 21 inches; the Mississippi Valley 
belt between 21 and 24 inches; and the Carolina and Georgia 
belt about 23 to 25 inches. 

250. Heavy rainfall. — Rainfall is frequently much heavier 
in the South than in most other sections of the country and 
there may be too much moisture as well as too little for the 
best development of cotton. In view of this, a satisfactory 
correlation is often impossible on the basis of a direct relation 
between rainfall and jdeld, that is by assuming that the 
greater the rainfall the larger the yield, as has been found to 



112 



AGRICULTURAL METEOROLOGY 



be the case during certain periods of corn development in the 
principal corn-producing area. To overcome this difficulty, 
Kincer has suggested that the amount of rainfall and degree 




Fig. 28. — Showing the relation of the mean temperature from May 1 to 
June 30 and the amount of cotton ginned in Georgia and Alabama 
to September 25. The solid line shows the departure from the 
average amount ginned in thousand bales and the dotted line the 
departure of mean temperature from the normal. 

of temperature necessary to produce a theoretical maximum 
crop be taken as a base with the assumption that departures 
therefrom would correspondingly reduce the yield. He con- 
cludes also that in the case of crops of this character in which 



WEATHER AND CROPS 113 

the growing period is long and in which no short critical pe- 
riod is in evidence, that much more satisfactory results can 
be obtained by giving certain weights to the departures of 
rainfall and temperatures to represent the modifying influ- 
ence of certain associated combinations of rainfall and tem- 
perature conditions, of the condition of the soil at the begin- 
ning of a month (or other period selected as a unit), and of 
intensified effect due to long sustained periods of unfavorable 
weather. 

251. Weather-cotton equation. — In working out a corre- 
lation of weather and cotton yield in the state of Texas, Kin- 

cer employed the equation X = d —, when "X" 

represents the yield of cotton in pounds to the acre; ''a " the 
departure of rainfall from the normal; ''b," the departure of 
temperature from the normal; ''c" and ''ci" weights to be 
applied to a and b; '^n," the number of months (in this case 
April to September, inclusive) and ^^d" a constant to repre- 
sent the number of points as computed from the rainfall and 
temperature departures from the normal to represent the 
average yield of cotton. The constant "d" in this case is 
necessary owing to the fact that the average rainfall and tem- 
perature would produce a cotton yield considerably above 
the average. 

The values Kincer assigned to the auxiliary factors c and 
Ci for the twenty-year period 1894 to 1913, inclusive, are 
given in the following tables. In Table 8 are entered the 
values for c, and in Table 9 those for Ci* These are of ne- 
cessity arbitrarily or empirically fixed, but were assigned 
after a careful study of weather conditions for the period 
named, in conjunction with the resulting yield for the respect- 
ive years, and from a general knowledge of the effect on plant 
development of certam combinations of weather. A careful 
study of the tables will disclose logical relations. 

Under rainfall there may be four conditions: (1) a month of 
plus departure following a month of like departure; (2) a 
month of plus departure following a minus departure; (3) a 
month of minus departure following a like sign ; (4) a month 
of minus departure following the opposite sign. The values 
assigned to c in each case are as follows: — 



114 AGRICULTURAL METEOROLOGY 

Table 8. — Rainfall Auxiliaries; Values for c 

Condition Apr.^ May June July Aug. Sept. 

1 + following Oor+ 4 8 8 4 4 4 

2 + following — . 4 4 2 ^ 2 ^ 2 2 3 

3 - following -1 4 5 6 8 » 10 » 8 ' 

4 - following Oor+ '2 2 3 6^ 8^ 4 

Under temperature there can likewise be four combina- 
tions: (1) a plus temperature departure occurring with a plus 
rainfall departure; (2) plus temperature departure with minus 
rainfall departure; (3) minus temperature with minus rain- 
fall departure; (4) minus temperature with plus rainfall de- 
parture. The values assigned to ci in each case are as follows: 

Table 9. — Temperature Auxiliaries; Values for ci 

Condition Apr. May June July Aug. Sept. 

1 +Temperature with or+ 

rainfall . 

2 ' +Temperature with — rainfall . . 

3 — Temperature wi th — rainfall ^ . 

4 — Temperature with-]- rainfall ^. 

It will be noted that prolonged periods of unfavorable con- 
ditions are provided for by increased values as indicated in 
footnotes. 

Kincer gave the constant "d" in this state a value of 100, 
which means simply that a total value of 100 points, as com- 
puted from the rainfall and temperature departures, repre- 
sents conditions favorable for production of an average yield 

1 Minus departures of less than 0.3 of an inch for April and May are 
considered as normal. 

2 If following two or more months of minus departure, substitute 1 if 
departure more than 1 inch; and if less than 1 inch. 

^ If fourth consecutive month of minus departure, increase value by 
2; fifth month by 6, and sixth month by 8; all minus departures for 
July and August of more than 2 inches are given a minimum value of 12. 

^ If third month of minus rainfall increase value by 2; if the fourth, 
fifth, or sixth month, by 3. 

^ If third consecutive month of minus temperature departure, in- 
crease value by 1; fourth month by 2; and fifth or sixth month, 
by 3. 



1 


1 


1 


1 


1 


1 


1 


1 


2* 


2' 


24 


14 


1 


3 


2 


2 


2 


2 


1 


4 


4 


2 


2 


2 



WEATHER AND CROPS 



115 



of cotton. When - 2 (ac + be) <d, X would be positive and 



when - S (ac + be) >d, X would be negative. 

252. Equation in Texas. — Kineer applied this equation 
to the weather conditions in Texas for the period from 18-94 
to 1913, for the months of April to September, inclusive, with 
a resulting correlation coefficient of +0.88 and a probable 
error of only =b 0.03. The actual results are shown in Table 10. 



Table 10.- 



-comparison of actual with computed departures op 
Crops from Normal Yield 





Actual 


Computed 


Years 


departures " 


departures 




Lbs. acre 


Lbs. acre 


1894 


65 


46 


1895 


— 19 


-14 


1896 


-64 


—64 


1897 


- 5 


34 


1898 


42 


47 


1899 


15 


8 


1900 


56 


- 9 


1901 


— 11 


— 6 


1902 


-22 


-20 


1903 


— 27 


-29 


1904 


13 


13 


1905 


- 6 


-10 


1906 


55 


54 


1907 


-40 


—44 


1908 


26 


24 


1909 


— 45 


-48 


1910 


-25 


-36 


1911 


16 


5 


1912 


36 


30 


1913 


-14 


-6 



253. General weather effects. — Cotton has the cliarac- 

teristics of a weed and due to this fact and also owing to the 
long season during which growth and fruiting take place, 
there seems to be no comparatively short period in the devel- 
opment of the crop in which unfavorable weather is likely to 
prove disastrous. . Whenever unfavorable weather prevails, 
the plant does not necessarily suffer permanent injury, but 



116 AGRICULTURAL METEOROLOGY 

improves rapidly with the return of good growing weather 
even after a long period of adverse conditions. 

254. Seasonal weather. — There are certain well-defined 
weather conditions, however, which hinder or promote 
growth. Rainy and cold weather early in the season hinders 
the preparation of the soil and the planting of the seed or 
proper germination; excessive rainfall in the first part of 
the season not only prevents proper cultivation, but encour- 
ages shallow root development; dry and hot weather later in 
the season is very detrimental. 

255. April should be warm and moderately dry especially 
in the central and eastern part of the belt, as cold and wet 
weather hinders planting and cultivation, and may make the 
crop so late that it is liable to receive frost damage in the fall. 
In Texas, however, low yields have been more frequent with 
a dry April than an April with the rainfall above the normal. 
Cool Aprils in this state are followed by more low yields than 
high ones. Kincer found that of fourteen years with com- 
paratively low cotton yield in Texas, nine of them had the 
average temperature for the state for April below the normal 
and five above normal. 

256. May. — In the central and eastern states. May 
should be warm and comparatively dry, as cool and wet 
weather retards growth and final maturity and prevents 
proper cultivation. 

257. June. — Cool and wet weather is harmful in June 
also as thorough cultivation is especially important owing to 
the length of time between the final chopping out period and 
the maturity of the last fruit, and the resulting tendency of 
the fields to become grassy. 

Kincer found that in Alabama the rainfall was above the 
normal from May 1 to June 30 in ten of the years from 1900 
to 1915 and in seven of these years the yield of cotton was be- 
low the average. The rainfall was above the normal in 
Georgia in May and June also and in these ten years the 
yield was below the average nine times. In Alabama of 
eleven years in which the temperature was below the normal 
in May and June, seven had yields below the average and 
four above, while for the eleven years in Georgia with cool 
weather during these two months nine had yields below the 
average and two above the average. 



WEATHER AND CROPS 



117 



258. July and August. — Subnormal rainfall during the 
months of July and August is more frequently harmful in the 
western portion of the belt than in the central and eastern 
parts, owing to the normally greater amounts received in the 
latter districts. In general, the yield of cotton is largely af- 
fected by the rainfall during the months of July and August, 



7 


























6 








• 




























• 






























{ 


• 




• 






• 


• 
• • 


•• 


• • 








• 


•• 


o 


• 


















/ 


• 


• ^ 


• 


























• 






















• 




















iti 


°/C 


70 12 


S It 


n 


'5 2L 


:o 


2. 


?5 


2. 


SO 


2. 


75 


30 



Fig. 29. — Relation between the rainfall in August and the yield of 
cotton in Texas, 1891-1918. 

especially the latter, but in the central and eastern parts of 
the belt temperature and moisture conditions during the 
early period of growth are of scarcely less importance. The 
influence of August rainfall in general, and especially in the 
western part of the belt, and the detrimental effect of cool 
and wet weather during the early growing season are indi- 
cated by the following. 

259. Rainfall in July and August not the controlling fac- 
tor in Texas. — That the rainfall for neither August nor for 



118 



AGRICULTURAL METEOROLOGY 



July and August combined are the controlling factors in the 
cotton yield in Texas is shown by Figs. 29 and 30. While 
there is a general increase in yield with an increase in rain- 
fall, the relation is only approximate and no good estimate 
of the yield can be obtained from a knowledge of the rainfall. 



/2 











? 


B 
/ 








A* 






/. 


• 
> 








• 




o / 




• 






MEAN 




••• 


/ •• 










• 


' • 


/ 


• 


• 








• 


/ 


> 


• 


• 


a- 118 
b' 10.13 
y-a-hbr 




A' 


/ 


i 










M.T. 



'WO 



125 



150 175 200 225 250 

YIELD OF COTTON- POUNDS 



275 



300 



Fig. 30. — Relation between the rainfall for July and August combined 
and the yield of cotton in Texas, 1891-1918. 

' 260. Winter rainfall and the yield of cotton in Texas. — 

The opinion is often expressed that the yield of cotton in Texas 
is largely dependent on the rainfall during the previous fall 
or winter. This belief seems to be disproved by Figs. 31 and 
32. These charts indicate that small cotton yields are about 
as frequent with heavy as with light autumn or winter rain- 
falls. Also that heavy yields frequently occur with light win- 
ter precipitation, due to favorable weather in the spring and 
summer. 

261. Some important comparisons. — For the sixteen- 
year period from 1900 to 1915, inclusive, the rainfall for 
August in Texas was normal or above seven times, and for 
these seven years the acre yield of cotton was above the six- 



WEATHER AND CROPS 



119 



teen-year average six times and below the average but once. 
For the nine years in which the August rainfall was below 
the normal, the yield was also below the average eight times 
and above the average once. For the same period in Alabama, 
the August rainfall was above the normal seven times, for 
which years the yield was above the average five times and 



/4.0 



%'"' 
^ 



%8. 



o 

1^. 







/ 


• 












• 
• 


















• 




< 


1 






• 

MEAN < 


• 


• 






• 








• 


• 














• • 


• 


• 

: 


• 


• 










• 






a- 168.345 
i?' 0.3334 
y^a+br 




• 




J 










W.7. 



JOO 125 150 175 200 225 250 275 300 

YIELD OF COTTON -P0UND5 

Fig. 31. — Relation between the rainfall from October to December and 
the yield of cotton in Texas during the following year, 1892-1918. 

below the average twice, while for the nine years with sub- 
normal August rainfall the yield was below the average seven 
times and above twice. In Georgia, however, this period had 
six years with August rainfall above normal, four of which 
had yields below the average and two above the average, but 
for the ten years with subnormal August rainfall the yield 
was below the average seven times and above the average 
three times. 

After the plants have attained their vegetative growth, 



120 



AGRICULTURAL METEOROLOGY 



the ripening of the fruit and seeds is favored by cooler 
nights. 

262. September and October. — The cotton is Hable to 
be beaten out and damaged by stormy weather after open- 
ing and while picking is going on. The amount of rainfall 
during the latter part of the growing season, particularly in 



/6 

14 
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J50 175 200 225 250 

YIELD OF COTTON - POUNDS 



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Fig. 



32. — Relation between the rainfall from November to March and 
the yield of cotton in Texas the following fall, 1892-1918. 



September, is also of special significance, as this largely de- 
termines the amount of the top crop, which plays a consider- 
able part in the total yield. A late fall with a delay in the 
first killing frost date also allows for the development of the 
top crop when not affected by weevil. 

263. The weather effects of two seasons compared. — 
The Weather Bureau publishes diagrams each year in the Na- 



WEATHER AND CROPS 



121 



tional Weather and Crop Bulletin indicating the combined 
effect of rainfall and temperature variations on the growth 
and condition of several of the most important crops. 

Figs. 33 and 34 are taken from these diagrams and show the 
effect of two quite different seasons on the condition of cotton 
in Oklahoma. Fig. 33 is for 1917, which was generally favor- 
able for cotton, and Fig. 34 for 1918 when a severe drought 
prevailed in the western cotton states. In 1917 May was very 
cold and cotton was unfavorably affected, but with more 



No. 1. Oklahoma. 


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Fig. 33. — Diagram showing the effect of the weather on the condition 
of cotton in Oklahoma in 1917. 

favorable weather later there was an improvement in all of 
the states except Texas, and the earlier handicap was almost 
overcome. The generous rainfall in August in Oklahoma as 
shown by Fig. 33 was especially beneficial to this crop. In 
1918 the weather during the spring was much more favorable, 
but drought and high temperature during most of the summer 
nearly ruined the crop in Oklahoma and Texas. The effect 
of these conditions in Oklahoma is especially shown in Fig. 
34. During these months wet weather reduced the outlook 
for cotton in the eastern part of the area. 



122 



AGRICULTURAL METEOROLOGY 



264. Insect pests. — ^Wet and cloudy weather favors the 
development of the boll-weevil, especially if wet enough to 



No. 1. Oklahoma. 




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Fig. 34. — Diagram showing the effect of the weather on the condition 
of cotton in Oklahoma in 1918. In the upper part of each of the 
diagram.s (Figs. 33 and 34) the heavy soHd line indicates the normal 
weekly rainfall, while the average for the state for each week is 
shown by the heavy upright line. The rainfall values are indicated by 
the figures at the left. In the lower part of each diagram the heavy 
horizontal line represents the normal temperature, while the variable 
black line shows the temperature for each week from the normal, as 
indicated by the figures at the left. The condition of cotton on the 
25th of the month, as compared with a ten-year average, expressed in 
percentages as shown by figures at the right, is indicated by the 
dots, and these are connected by broken lines. 

hinder cultivation; while in the eastern part of the belt, hot 
dry weather hastens the development of red-spider. 

265. Boll-weevil and temperature. — With a mean 
monthly temperature of 60°, the activities of the weevil are 
greatly reduced. Investigations by the Bureau of Entomol- 
ogy, United States Department of Agriculture, show that an 



WEATHER AND CROPS 123 

exposure to a temperature of 20° for a period of six hours is 
fatal to the boll-weevil. It is probable, therefore, that when- 
ever the winter temperature reaches a minimum of 10°, the 
weevil will be greatly reduced in all districts and almost en- 
tirely killed out in prairie sections, where there is less protec- 
tion than m wooded areas. If only a few escape death how- 
ever, they may multiply so rapidly with favorable weather 
in the spring and summer as to cause great damage, although 
the damage will be later than if the winter is mild. 

The following statement by L. O. Howard is of interest in 
this connection: 

The most important climatic factors which affect the boll-weevil are 
wmter temperatures and spring precipitation. Naturally low winter 
temperatures reduce the weevils enormously in numbers, while high 
sprmg and early summer precipitation has the effect of increasing their 
numbers. It has been found in observations made during several sea- 
sons that no accurate forecast of weevil conditions during the summer 
can be made from winter mortality. Attempts to do this were made in 
the early days of the mvestigation of the weevil, but we have been forced 
to abandon further attempts. On several occasions the weevil has been 
decimated by low winter temperatures but wet weather the following 
May and June negatived the conclusion of summer scarcity which would 
appear to be warranted by the winter conditions. In a similar way the 
survival of an enormous number of the weevils through mild winters 
has not resulted in any proportionate damage of the crop, on account 
of dry weather during May and June. 

266. Boll-weevil and rainfall.— The most important 
single factor in holding the weevil in check is dry weather dur- 
ing the growing season, as dryness increases the death rate 
of immature weevil in the fallen squares enormously. 

267. Wind and spread of weevil.— The normal advance 
of the boll-weevil into new territory is 50 miles a year, but 
high winds, with other conditions favorable, may cause a 
much more rapid spread of this insect, as was the case from 
August 15 to 31 in 1915 when they advanced fully 100 miles. 

Flax 

Flax for fiber is grown in regions in Europe with high hu- 
midity, moderate rainfall, and rather cool and uniform sum- 
mer temperatures, as even and rather slow growth is neces- 
sary to produce a long, even, fine fiber. Anything that checks 



124 AGRICULTURAL METEOROLOGY 

the steady growth of straw during the period preceding boll 
formation is sure to result in an inferior type of fiber. In 
Egypt, the beginning of flax-culture dates back to 4000 B. C. 

268. In North America. — Flax is grown mostly for seed 
in this covuitry and principally in the Dakotas and Min- 
nesota and the adjoining Canadian provinces. In this sec- 
tion of the United States, the annual rainfall is 15 to 20 
inches and the rainfall during its growing season of 80 to 110 
days is from 10 to 12 inches. As this is a region of rapid tem- 
perature changes and uneven rainfall, the straw is short and 
coarse and the fiber is uneven, hence only seed is produced. 
For the best development for seed also a steady even growth 
is desirable with only sufficient moisture to cause a sturdy 
type of stem growth and a heavy production of foliage. 

Very recently the cultivation of fiber flax is becoming an 
established industry in eastern Michigan and the Willamette 
Valley in Oregon. 

269. Moisture and flax. — Too much moisture results in 
a weak and imperfect stem and poor boll and seed formation. 
A severe drought near the time of flowering or boll formation 
will cause a hardening and ripening of the straw, especially 
of the slender stems on which the bolls form, thus cutting off 
the proper supply of food materials. 

Hot dry winds and a lack of moisture when the plants are 
in bloom are detrimental to the seed crop, while cool and 
cloudy weather causes it to bloom for a long time and hence 
to ripen unevenly. Cool nights, fairly warm days, with 
plenty of moisture are conducive to extensive branching. 

270. Frost effects. — A shght frost after flax has reached 
a height of 2 inches may not injure the plant, but if it is cut 
off by frost at a point below the first or "seed" leaves, the 
plant loses its power of growth. 

271. Flax in North Dakota. — Warm weather with some- 
what less than the normal rainfall during May and June, 
while planting and germinating are going on, produces the 
best condition for flax in North Dakota. The best results 
have been obtained with wet and warm weather in August, and 
wet and cool in early September. The maturing period falls 
in August and the first of September so it is necessary to have 
plenty of moisture to fill out the seed well. 

The seeding of flax is mostly done in this state during the 



WEATHER AND CROPS 125 

last half of May and the first half of June, although seeding 
may be continued until the middle of July. The crop is har- 
vested in the latter part of August, September, and the first 
part of October. 

Hemp 

Hemp is cultivated in warm countries for the production 
of a narcotic drug, but in moist temperate climates such as 
the central part of the United States it is cultivated for fiber. 
It is one of the oldest fiber-producing crops, and is important 
in Japan, China, and India. 

272. In the United States. — The principal hemp-produc- 
ing districts in the United States are in central Kentucky 
and in parts of Wisconsin. Practically all the hemp seed 
in the United States is produced on narrow strips of land 
between the bluffs, along the Kentucky River. 

273. Growing season. — In fiber production, the seed is 
planted about the 10th of April in Kentucky and the growing 
season is about 130 days. For seed, it is planted somewhat 
earlier and harvested in the first part of October. 

274. Temperature. — Hemp grows best where the tem- 
perature ranges between 60° and 80°, but it will endure higher 
or lower temperatures. Light frosts will not greatly injure 
either the young or mature plants for fiber, but a frost before 
harvest will greatly damage the plants for seed. 

275. Rainfall. — The most critical period of growth is 
shortly after it comes up, when it must have plenty of mois- 
ture, as a period of dry weather at this stage may cause great 
injury. 

FRUITS 

The climate should be carefully considered in the growing 
of fruit. The prevailing weather also influences the yield to 
a marked extent. The fruits will be discussed separately. 

Almonds 

(These nuts are classed with fruit in California.) Almonds 
are the first of the deciduous fruit-trees to start to grow and 
to bloom in the spring and the last to lose their leaves in the 
fall. Its period of dormancy in this climate is very short, usu- 
ally being complete only during December and January. 



126 AGRICULTURAL METEOROLOGY 

276. Temperature and almonds. — The almond tree is 
hardy and will endure fully as much cold as the hardiest peach 
without injury. The blossoms on the other hand are very 
tender, and even when there is an entire absence of frost dur- 
ing blooming, sudden marked changes in temperature may 
greatly damage or ruin the crop. The most tender stage in 
the blossoming and development of the young fruit seems to 
be that immediately following the dropping of the calyx-lobes 
as the fruit first commences to swell rapidly. 

277. Moisture and almonds. — Continued rainy, damp, 
and cold weather at the time of blooming is likely to sour the 
pollen or actually wash it away. Foggy or moist weather dur- 
ing ripening or harvesting is very objectionable. 

Ayjples 

In the eastern part of the United States, the area of exten- 
sive apple-culture does not extend south of the mean summer 
isotherm of 79°, or north of the mean winter isotherm of 13°. 
There are few orchards in the Great Plains states west of the 
18-inch annual precipitation line. The leading apple states 
are New York, Michigan, Pennsylvania, and Missouri. 

278. Weather and apple yield. — A study of the effect of 
the weather of different months on the yield of apples was 
made for Belmont County, Ohio, covering the period from 
1889 to 1910. This showed that the most important months 
were February, of the current year, and June of the previous 
year. 

279. February. — In the twenty-one years, the apple crop 
was always below the normal when February was warm and 
wet and usually above the normal when it was cool and dry. 
The correlation coefficient between temperature and yield 
was — 0.51 and between the rainfall and yield, — 0.50, the 
probable error in each case being ±0.10. 

280. March. — Wet weather in March was also detri- 
mental, especially if warm, and cool and dry weather was fa- 
vorable although these conditions were not so well marked 
as in February. 

281. Other months. — No marked relation was shown 
between the yield and the weather in April, May, June, July, 
or September. August, however, should be warm and wet 
for best results. A comparison of the yield with the mean 



WE AT ITER AND CROPS 



127 



monthly temperature and precipitation of the previous year 
showed no relation with May or July conditions. It did show 
that dry weather in August was detrimental although a wet 
August was not always followed by a good jdeld. A cool and 
wet June, however, was always followed by a yield below the 

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Fig. 35. — Combined effect of the weather of June of the preceding year 
and February of the current year on the yield of apples, Belmont 
County, Ohio, 19 years. 

normal the next year while a dry and warm June usually pre- 
ceded a good crop the following year. 

282. Fruit and leaf development. — As the fruit-buds de- 
velop in the preceding year and as wet weather favors active 
extension growth which is produced at the expense of fruit- 
bud formation, it follows that a dry and warm June should 
be favorable for the formation of a good number of fruit-buds 



128 AGRICULTURAL METEOROLOGY 

for the next year's crop. A good rainfall in June produces a 
large amount of soil-moisture during succeeding weeks or 
months when the buds are developing, thus making a prepon- 
derance of extension growth and thus a larger percentage of 
branch and leaf-buds and a smaller percentage of fruit-buds. 

283. Combined effect of June and February. — As a warm 
and dry June of the preceding year and a cool and dry Feb- 
ruary of the current year are both favorable for a good yield 
of apples, these conditions have been combined in Fig. 35. 
It should be noticed that in this chart the February tempera- 
ture values have been reversed so that a warm June is grouped 
with a cool February. When the rainfall for the two months 
combined was above the normal, the yield was always below 
normal, and when below the normal the yield was above the 
norinal eight times in ten. A correlation of the yield with the 
combined rainfall for June of the preceding year and Febru- 
ary of the current year gave a correlation coefficient of — 0.60 
(probable error ±0.10), and with the average temperature 
(with the February temperature departures reversed) gives a 
correlation coefficient of -|-0.48, with a probable error of =t 0.11. 

284. August and February combined. — In Fig. 36 the 
weather of August of the preceding year and February of the 
current year were combined in a similar manner. It must be 
noted that a dry August is combined with a wet February by 
reversing the values so that a wet February is grouped with 
a dry August. In the thirteen years when the departure of 
these combined rainfalls, after reversing the August values, 
was above the normal, the yield was below the normal every 
year but one. 

285. Combined precipitation for June, August, and Feb- 
ruary. — On combining the departure of the precipitation 
for June of the preceding year and February of the current 
year above the normal with the rainfall for August of the pre- 
ceding year below the normal, the correlation with the yield 
gave a coefficient of — 0.62 with a probable error of =i=0.09. 

286. Apple diseases. — Bitter-rot or ''ripe" rot of apples 
is a typical hot weather disease. It is serious in the more 
southern apple districts. Hot and wet weather with the pre- 
vailing temperature above 80° produces conditions favorable 
for its spread. A local shower on a hot July afternoon may 
supply just the right condition when the whole crop may be 



WEATHER AND CROPS 



129 



destroyed in a week. The outbreak may be checked by a few 
days of cool weather with the mean temperature below 70°. 

Special forecasts of weather conditions favorable for the 
spread of this disease should be made by the Weather Bureau 
and distributed as in connection with the apple-scab, so that 
spraying may be done at the proper time. 

287. Codlin-moth.— Warm and dry weather favors the 
development and multiplication of this apple pest. The be- 



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Fig. 36.— Combined effect of the weather for August of the preceding 
year and February of the current year upon the yield of apples, 
Belmont County, Ohio, 19 years. 

ginning of emergence in the spring is hastened by high tem- 
perature in March, April, and May. In the state of Washing- 
ton it is known that the codlin-moth does not become active 
unless the temperature is 60° or higher. In other words, no 
breeding takes place when the temperature drops below 60°. 

Apricots 

288. Apricots thrive best in the hot valleys of the South- 
west. The fruit ripens at a time of the year when the rela- 
tive humidity is at its lowest point and the danger of showers 
least, consequently the conditions are the most favorable for 
drying the fruit. They receive little injury from either the 



130 AGRICULTURAL METEOROLOGY 

frosts of spring or the heat of summer, compared with apples 
or plums. 

Avocado or alligator-pears 

289. This is a tropical or semi-tropical fruit. The fruit 
of the hard-shelled type requires over a year to mature. Some 
varieties will stand from 5° to 10° below freezing. Strong 
winds are often damaging. 

Cherries 

Cherry trees do not thrive as a rule in the southern states 
where the summers are long and hot. The southern limit is 
not quite so far south as that of apples. The northern limit 
of sour cherries approaches that of apples while sweet cher- 
ries are slightly less hardy, corresponding more nearly to the 
peach. The fruit-bud formation in some cherries begins 
about July 1, of the previous year, in central latitudes. 

290. Weather and cherries. — Some preliminary studies 
in Ohio indicate that if February is wet it should be cool and 
if warm it should be dry for best results. April should be cool 
and wet. In May cool weather is more favorable than warm, 
and in June moderately dry weather is more favorable than 
wet. 

Currants and gooseberries 

291. Both currants and gooseberries are natives of cool, 
moist northern climates and succeed best in the United States 
in the northern half of the country east of the 100th Meridian. 
They are injured by the long hot summers of the southern 
states, except in the higher altitudes of the Appalachian 
Mountains. Gooseberries are grown slightly farther south 
than currants. Both plants are very hardy and withstand 
extremely low temperatures, but as they blossom very early 
they are subject to frost damage. 

Cranberries 

Cranberries are indigenous to marshes, chiefly in the nor- 
thern states, although wild cranberries are found at consider- 
able elevations on moist mountain-sides in New England. 
Cranberries are cultivated intensively only in Massachusetts, 
New Jersey, and Wisconsin. 



WEATHER AND CROPS 131 

292. Cranberries and temperature. — The vines are sub- 
ject to winter-killing and when water is available the cran- 
berry^ bogs are kept covered during the winter months. While 
frost is not often experienced in the summer months in the 
eastern states, it may occur during any month in the low- 
lying bogs in Wisconsin. The minimum temperature in the 
cranberry bogs may be from 5° to 15° lower than on the sur- 
rounding slightly higher ground. 

293. Protection from frost. — Cranberries are protected 
from light frosts by raising the water in the ditches that run 
through the bogs, but the vines must be entirely covered by 
flooding to protect from severe frosts. 

Dates 

294. Dates require intense summer heat and dry air, but 
will bear abundant crops only when well irrigated. The 
plants make their most rapid growth during the warmest part 
of the year. The dormant mature trees will endure an occa- 
sional temperature considerably below freezing, but there will 
be no development of the flowers or fruit when the tempera- 
ture is below 64°. Even a light rain after the fruit has begun 
to ripen is very damaging. The date harvest season in Cali- 
fornia is in September and October. 

Figs 

295. Fig-growing is confined primarily to regions where 
the winters are comparatively mild. They are injured or 
killed to the ground by temperatures that do not affect most 
other fruits of the temperate zone when in a dormant condi- 
tion, especially when young. As the trees get older, they be- 
come less subject to winter-injury, and in Arizona are rarely 
injured by the cold of winter or the heat of summer. 

Grapes 

Grapes are raised in the United States principally in Cali- 
fornia, western New York, northern Ohio, and southwestern 
Michigan. Most of the raisins used in the United States are 
grown in the Fresno district of California. 

296. Temperature and grapes. — Winter-killing of grapes 
can be traced to a lack of maturity in the fall. An index to 



132 AGRICULTURAL METEOROLOGY 

this immaturity is the incomplete ripening of the crop as 
shown by high acidity and low content of solids, especially 
sugar. A warm rainy September and a cool cloudy October 
leave the vines soft and succulent and give poor conditions 
for proper ripening of fruit. If these conditions are followed 
by marked temperature variations during the winter, the 
crop of the next year is likely to be poor. 

297. Critical temperatures. — When the vines are well 
matured, they will withstand a winter temperature of at least 
25° below zero. It was found in New York that the danger 
point in the winter is between - 26° and — 30°. When in bud 
bloom, and setting fruit, the critical temperature is 31°. The 
leafing of some native varieties occurs after ten or twelve days 
with a daily mean temperature of 52° to 53°. If freezing 
weather follows, the leaves and young growth will be killed 
and although they will grow new vines the crop will usually 
be reduced. 

298. Weather and grapes. — A study of the effect of 
weather on grapes in northern Ohio showed that for best re- 
sults, February and March should be dry and moderately 
cool, as wet and warm weather hastens growth and causes 
danger from later frosts. April should be moderately dry and 
warm as wet weather interferes with fertilization and anthrac- 
nose develops in cool and wet weather. May should be wet 
and warm to bring about vigorous growth. The grapes bloom 
in June in Ohio and a cold northeast wind or storm prevents 
pollination. Periods of warm sultry weather in June or July 
followed by dry warm weather may start the mildews and 
black-rot. A normal rainfall is needed in August and Sep- 
temper to develop the fruit and there should be plenty of sun- 
shine. Warm weather with sunshine is necessary in the fall 
to allow for late picking. 

299. Sugar-content. — In northern Ohio the sugar-content 
of white and Catawba grapes increases the longer they are 
left on the vines in the fall, consequently the growers delay 
picking as long as possible. Warnings of cold weather 
or sleet storms are desirable at this time to hasten pick- 
ing. In the hot valleys of southwestern Europe, grapes 
have a very high sugar-content and although they ripen 
early they sometimes become very sweet before they are 
ripe. 



WEATHER AND CROPS 133 

Olives 

300. Temperature. — The olive is very drought-resistant. 
Its range is restricted by temperature, although there is con- 
siderable difference in the varieties in the resistance to cold. 
In California, the winter mean temperature where olives are 
grown should not be below 48° and the summer mean should 
seldom exceed 80°. The dormant trees should not be sub- 
jected to a temperature below 15° to 20° and seldom below 
28° or 30°. The fruit is very sensitive to frost and is seri- 
ously injured by a temperature of 28° even for a short time. 
The trees require a mean annual temperature of about 57°, 
and a mean temperature of over 66° for several months, at 
least during the first of the season, seems necessary. They 
blossom in an average year when the mean daily temperature 
reaches 66°. 

Olives are peculiarly well adapted to southern Arizona 
where they are not injured by the heat of summer and very 
rarely is the fruit damaged by the cold of winter. 

Peaches 

Peaches are raised most extensively in the United States 
from northeastern Texas and Arkansas eastward to the At- 
lantic Coast and northeastward to the lower Lake region, and 
in California. About three-fourths of the peach trees are 
south of the Ohio and Missouri rivers and in California. The 
mean winter isotherm of 25° is a fairly well-defined northern 
limit for extensive peach production. 

301. Temperature effects. — When thoroughly dormant, 
peach-buds will withstand a temperature of 12° to 20° below 
zero (F.), depending somewhat on the variety. Thorough dor- 
mancy is, however, somewhat indefinite and not very con- 
stant. Peach-buds are advanced easily by short spells of 
warm weather in even late fall or early winter and will then be 
killed by temperatures only slightly below zero. 

302. Critical temperatures in Missouri (Chandler). — The 
killing temperature of peach blossoms when the tree is just 
coming into full bloom, under Missouri conditions, seems to 
vary from about 22° to 26°. After the blossoms are old 
enough so that they are probably pollinated, and from that 
time until the peaches are as large as half an inch in diame- 



134 AGRICULTURAL METEOROLOGY 

ter, they continue to grow more tender until they will with- 
stand but a few degrees below 32°, the seeds of the young 
peaches killing at a higher temperature than other peach tis- 
sue. The length of time subjected to the low temperature is 
an important factor. 

303. Temperature and peach trees. — Thoroughly dor- 
mant peach trees will usually stand a temperature of 5° to 10° 
lower than the buds. The injury to trees depends, however, 
on the condition of the trees, the duration of the cold, the 
soil and surface cover, and the rapidity of thawing. 

304. Moisture and peaches. — Like other stone-fruits, 
peaches require plenty of moisture for proper development. 
The Utah Agricultural Experiment Station Bulletin No. 142 
states that ''No amount of water applied early in the season 
to a crop of peaches on gravelly soil will compensate for the 
lack of water during the month before harvest." 

305. Weather and the yield of peaches. — Quite extensive 
studies of the relation between the mean temperature and 
total rainfall for different months and the yield of peaches in 
northern Ohio have given no well-defined correlation. 

306. Diseases of peaches. — Leaf-curl in Ohio is developed 
by cool, rainy, and cloudy weather. It is said that profitable 
spraying may be predicted with fair certainty from a knowl- 
edge of the temperature and rainfall in the first half of April. 
Warm moist weather conditions during May and June appear 
to be especially favorable to the development of the peach- 
scab fungus in New Jersey. 

Pears 

307. Pears are raised most extensively in the north- 
eastern part of the country, in the Pacific states, and in a 
small area in western Colorado, although many are grown in 
other districts except in the upper Mississippi and Missouri 
valleys and in the central ,and upper Great Plains. 

Plums 

308. Plum trees of different varieties are widely scattered 
over the eastern half of the country, but the most intensive 
development of this crop, particularly the variety that is dried 
for prunes, is in central California. Plums thrive best in an 



WEATHER AND CROPS 135 

equable climate with a long growing season, plenty of sun- 
shine, freedom from frosts and from early fall rains and fog. 
They cannot endure extremes of heat and cold and of wet 
and dry weather. 

Prunes are a variety of plum that can be dried without the 
removal of the pit, without fermenting. ''All prunes are 
plums, but all plums are not prunes." 

Strawberries 

Strawberry cultivation is widely distributed, but the largest 
intensive areas are in southern New Jersey and eastern Mary- 
land and in northwestern Arkansas. 

309. Moisture and strawberries.— The plants need an 
ample supply of moisture in the soil constantly during the 
growing season and particularly while bearing fruit. 

310. Temperature effects.— The blossoms are injured by 
a temperature below 30°. The young fruit endures a tem- 
perature below 24° at the ground and green fruit lower than 
this. The ripening fruit endures less cold. Moderate tem- 
perature and comparatively dry weather is desirable during 
the harvest season. High maximum temperatures during 
blossoming are detrimental as it prevents the setting of fruit. 

311. Harvesting.— The average date of harvesting the 
crop is as follows: 

South-central Florida Dec. 1 to April 1. 

North Florida Feb. 10 to May 15. 

South Texas March 1 to May 15. 

South Louisiana March 15 to May 20. 

North Gulf and South Atl. Coast April 15 to June 1. 

Lower Ohio Valley and 

Northern Maryland May 15 to June 20. 

Southern New England 

and lower Lake region June 1 to July 15. 

312. Adaptation to climate (Farmers' Bulletin No. 1043). 
— ''In the selection of a variety for a given locality one should 
first determine whether it is suited to its climate. Thus, the 
Missionary, which is a good shipping variety in central Flor- 
ida, is not a good shipping variety in the upper Mississippi 
Valley. In the southern States the Missionary and Klondike 
make a quick growth in early spring, producing large crops 



136 AGRICULTURAL METEOROLOGY 

of early berries and in those parts of the South suited to them 
they are excellent shipping sorts. Neither of them, however, 
is adapted to the climatic conditions found in the northern 
states. In like manner, the Dunlap, a leading northern sort, 
is not adapted to southern conditions; when grown there it 
is too soft for shipping and sometimes too soft even for local 
markets. 

''Other varieties, such as the Glen Mary, Belt (William 
Belt), and Marshall, which are grown to a considerable ex- 
tent in the northeastern States, are not adapted to conditions 
farther south because of their greater susceptibility to leaf- 
spot diseases. The Clark, Jucunda, and other varieties grown 
in the dry atmosphere of the irrigated sections of the West 
are not grown in the East, and whether they would do well 
under the humid conditions in eastern sections is perhaps 
doubtful. It is important, therefore, to know the climatic 
adaptations of the different varieties before selecting them for 
extensive planting." 

313. Strawberry diseases. — Leak, caused by Rhizopus 
nigricans is by far the most important rot of strawberries 
after picking. It develops very slowly at 50° but increases 
rapidly with higher temperature. Berries picked early in the 
morning are cooler and will ship better than those picked near 
the middle of the day. Botrytis sp. is a field rot of strawber- 
ries that is most abundant and serious under conditions of 
excessive moisture. 

Citrus fruits 

Citrus fruits are of tropical origin and the intensive culti- 
vation of oranges, lemons, grapefruit, and limes is generally 
confined to places without severe frosts. They are success- 
fully grown, however, in regions in California where frosts oc- 
cur, although artificial protection from low temperature dam- 
age is usually resorted to. 

314. Oranges. — The most extensive orange orchards in 
the United States are in central Florida and southern Califor- 
nia, although they are raised in central California and in the 
Gulf coast districts of Texas, Louisiana, Mississippi, and Ala- 
bama. It has been found in California that the ripe orange 
begins to freeze when the temperature of the fruit itself 
reaches 28° F. The rind freezes first and the rapidity with 



WEATHER AND CROPS 137 

which the freezing extends inward depends on the air tem- 
perature and radiation. The temperature of the fruit lags 
from one to two and one-half hours behind the air tem- 
perature, depending on the rate at which the air tempera- 
ture falls. When the temperature is falling rapidly, that of 
the fruit is sometimes 7° higher than that of the outside 
air. 

315. June drop of navel oranges. — Navel oranges grown 
in the interior valleys of California and Arizona are subject 
to a large shedding of young fruit usually called "June drop" 
although it may occur at any time from the petal-fall in 
April to maturity. The period from petal-fall until the fruit 
is about 1 inch in diameter is the most serious. While this 
drop increases with high average daily temperature, many 
practical orchardists in California believe that the amount of 
the June drop depends primarily on low temperature during 
the preceding winter and secondly on the high temperature 
in summer. 

316. Oranges in Florida. — The annual growth of oranges 
in Florida is divided into four well-defined periods: (1) when 
spring blossoms are appearing and the young fruit forms. 
This is the most critical time from a moisture standpoint as 
dry weather may cause the young fruit to drop. (2) During 
the summer when fruit takes on size. Rain is needed, as a dry 
period may do serious harm by preventing fruit from attain- 
ing full size and color. (3) Fall and early winter when fruit 
is maturing and harvest begins. A severe cold wave at this 
time may cause great damage by freezing. (4) Dormant sea- 
son which is usually through December and January. 

317. Lemons. — The principal lemon district is in south- 
ern California. The lemon is more tender than the orange 
and the fruit is injured at 26° to 28°, and sometimes at even 
higher temperatures. Young small sized fruits, ''button 
lemons" are more tender than those large enough to harvest. 
The damage to lejnon trees by winter cold depends in a large 
degree on the age of the trees. Trees five years old have been 
frozen to the ground with a temperature of 19°, while old 
trees were not seriously injured. 

318. Limes are raised in Florida and California. They 
are more tender than lemons and the fruit is killed at temper- 
atures of 28° to 30°. 



138 AGRICULTURAL METEOROLOGY 

319. Pomelos (grapefruit). — The grapefruit trees are more 
hardy than the lemon but are more tender than orange trees. 
The fruit is not so easily frozen as are oranges. 

Te7nperatures withstood 

320. Critical frost temperatures for fruit. — ^The tempera- 
ture at which fruit-buds will be killed depends on so many 
factors that no well-defined limit can be designated. The con- 
dition of the tree, the stage of advance of the buds or blos- 
soms, their position on the tree or limb, the moisture in the 
atmosphere, the length of duration of the low temperature, 
and the previous weather that the tree has been subjected to, 
all enter into the problem of frost damage. 

321. Percentage of damage. — It has been pointed out 
that there is a range of at least 5° between the temperature 
at which all of the buds will be killed and that at which only 
5 per cent will be lost. If there are few blossoms on a tree, 
the critical temperature, therefore, will be higher than when 
it blossoms so freely that a large percentage can well be lost 
and yet leave as many as should develop fruit. As a usual 
thing, if only 2 per cent of the live buds of peaches remain to 
mature, it will mean a fair crop of fruit. It is frequently said 
that a fruit-tree in an average year should lose about 90 per 
cent of its buds or blossoms. 

322. Critical temperatures relative. — The critical frost 
temperature then is a relative term depending on the per- 
centage of blossoms that need to be saved from loss. 

323. Safe temperatures. — The following table gives what 
are believed to l^e safe temperatures for the normal tree in an 
average season under usual conditions. Under some condi- 
tions it is known that the temperature may fall several de- 
grees below these values without serious loss. In general, how- 
ever, when protection by heating is practiced, it is wise to 
prevent the temperature going below the point indicated for 
any great length of time. The figures are from observations 
by a number of experts or from actual tests by men of author- 
ity. 

Careful records of minimum temperatures and amount of 
damage on cold nights should be kept for future reference by 
every orchardist, especially if heating is done. 



WEATHER AND CROPS 139 

Table 11. — Probably Safe Temperature for Different Fruits 

Buds show- In full 

Kind of fruit ing color bloom Fruit setting 

Apples 27 29 30 

Apricots 30 31 32 

Almonds 28 30 31 

Blackberries 28 28 28 

Cherries 25 28 30 

Grapes 31 32 32 

Lemons — 32 30 

Pears 28 29 30 

Peaches 25 28 30 

Plums 30 31 31 

Primes 30 31 31 

Oranges 30 30 — 

Raspberries 28 28 28 

Strawberries 28 28 28 

324. The orange tree when fairly dormant will stand a 
temperature of 25° to 26° for an hour or so. At 20° to 22° the 
twigs begin to die back and the leaves fall. At 17° to 18° for 
four to five hours, the branches will be killed back to 2 or 3 
inches in diameter, unless the trees are quite dormant. 

325. Peaches. — West and Edlefsen in freezing experi- 
ments in Utah in which by an ingenious device they were able 

o freeze the buds on a detached limb or on the whole tree, 
-jund that the temperatures which will kill about 50 per cent 
buds of the Elberta peach are as follows: 

When slightly swollen, 14° 

: " well " 18° 

" showing pink, 24° 

" full bloom, 25° 

" setting fruit, 2S° 

J26. Cranberries. — Careful records in Massachusetts 
show that in the greenish white stage that immediately per- 
cedes the ripening of fruit, the berries will endure a tempera- 
ture of 26° without harm, and 25° with little injury, but 24° 
seems to harm such fruit greatly if it continues long. 

327. Dormant period. — In the northern part of the 
United States, fruit-trees should stop growing early so as to 
become fully dormant before th^ low temperatures of late 



140 AGRICULTURAL METEOROLOGY 

fall and winter occur. In the southern states, however, where 
little or no damage occurs during the dormant period, the 
problem is to keep the fruit-trees growing as late as possible so 
that the short dormant period will carry the trees through 
the spells of warm winter weather. Otherwise the buds de- 
velop too far and are killed by later cold. 

328. Most susceptible period. — It is believed that the 
peach is the least resistant to cold when it is about the size of 
a pea, when the calices are falling. The seed kills at a higher 
temperature than other plant tissue. After setting, the dam- 
age to young apples is due to the freezing of the stems. 

329. Weather and the setting of fruit. — Warm dry sunny 
weather is most favorable for the setting of fruit while cold 
and rainy weather is detrimental. Rain prevents bees and 
insects from- carrying the pollen while the secretion on the 
stigmas or the pollen on the anthers may be washed away, or 
the pollen-grains may swell and burst. 

330. Temperature effects. — In very warm weather the 
stamens, or male part of the blossom, will develop more rap- 
idly than the pistil, or female organ. Thus under high tem- 
peratures the stamens may be forced so much faster than the 
pistil that the pollen is shed before the pistil is ready to re- 
ceive it. In cool weather the pistil develops most rapidly. 
The pistil is often injured by a light frost that does not affect 
the stamens. It has been determined that the pollen of the 
apple will withstand much lower temperatures than will any 
other tissue of the flower when in full bloom. 

331. The killing of plant tissue. — During freezing weather 
ice forms in the inter-cellular spaces of the plant tissues and 
withdraws the water from the protoplasm in the plant-cells. 
It was formerly taught that if plants thawed slowly enough 
so that the cells could reabsorb the moisture as fast as the 
ice melted, little harm would result. Chandler and others 
have demonstrated from experiments, however, that the rate 
of thawing does not have anything to do with the amount of 
killing, at a given temperature. 

332. Frost is most damaging when fruit is wet. — A plant 
tissue with a wet surface kills worse at a given temperature 
than tissue with no moisture on the surface. 

333. Sun-scald on the southwestern or sun-exposed side 
of the trees is brought about by some interaction of sun and 



WEATHER AND CROPS 141 

cold in late winter, and is common in northern districts. The 
injury occurs late in winter or early in spring when warm days 
are followed by cool nights. The bark is subjected to rapid 
and extreme temperature changes, becomes unhealthy, dies, 
dries up, and falls away. It is prevented by spraying or 
painting trunks with whitewash. 

LABORATORY EXERCISES 

The possibilities of personal investigation on the part of the student 
are self-evident in Chapters VII, VIJI and IX. 

Each student should be given some specific crop, plant disease, or in- 
sect, and directed to show the relation between the weather and its de- 
velopment from past records. 

At the proper season valuable information can be obtained by noting 
the effect of current weather on crops, particularly fruit or truck. 

REFERENCES 

Fiber Crops 

Correlation of Weather Conditions and Production of Cotton in Texas. 
J. B. Kincer, Monthly Weather Review, February, 1915. 

Forecasting the Yield and the Price of Cotton. Henry L. Moore, The 
Macmillan Co., 1917. 

Hemp. L. H. Dewey. Yearbook, 1913. 

Some Recent Studies of the Mexican Cotton Boll Weevil. W. D. Hun- 
ter, Yearbook, U. S. Department of Agriculture, 1906, pp. 313-324. 

Fruit 

Almond in California, The. R. H. Taylor, California Experiment Sta- 
tion Bulletin No. 297. 

California Division of Agricultural Education Extension Courses, 1918. 

Currents and Gooseberries, Farmers' Bulletin No. 1021. 

Drought Resistance of Olives in the Southwestern States. S. C. Mason, 
Bureau of Plant Industry, Bulletin 192. 

Experiment Station Work with Peaches, Annual Report of Experiment 
Stations, 1906. 

Frost and Temperature Conditions in the Cranberry Marshes of Wis- 
consin. H. J. Cox, Bulletin T, U. S. Weather Bureau, 1910. 

Frost and the Prevention of Damage by It. Floyd D. Young, Farmers' 
Bulletin, 1096. 1920. 

Strawberries, Varieties in the United States, Farmers' Bulletin 1043. 

U. S. Department of Agriculture Bulletin 462. 



CHAPTER VIII 

THE EFFECT OF WEATHER ON THE YIELD OF 
GRAINS 

The bread and feed grains are the fundamental crops, aside 
from the earth-cover of grass. The yields of them are major 
factors in determining the financial movements of the year, 
and the quotations on them figure largely in stock exchanges 
and price-currents. The relations of weather and climates 
to these crops is a question of large public concern. 

BARLEY 

Spiking barley has. a» shorter growing., season than either 
wheat or oats and is cultivated farther nortii and at higher 
altitudes than other cereals. It is grown up to latitude 70 
degrees in Norway and to 653^2 degrees in Alaska. It ripens 
in 80 to 95 days after seeding in Alaska, and in about the 
same time in Wisconsin. 

334. Range in the United States. — The main spring bar- 
ley districts are in Wisconsin, Minnesota, North Dakota, 
South Dakota, and California. Some winter barley is grown 
in the South. 

335. Temperature and barley. — While some varieties of 
barley are grown on the tropical plains of the Ganges and in 
the hot districts of northern Africa, most of the crop in the 
United States is grown in a cool region. It serves as a crop 
where it is too cool for corn. All of the principal barley dis- 
tricts in this country do not have any month during the season 
of growth with the mean temperature above 75°. It has been 
found in England that the chief requirement as far as yield 
is concerned, is a cool summer, especially after mid-June. It 
is affected by spring frosts more than either wheat or oats 
but recovers quickly. Winter barley is not so hard}^ as win- 
ter wheat or rye. 

142 



WEATHER AND YIELD OF GRAINS 143 

336. Rainfall and barley. — The principal barley-growing 
districts of the United States receive an annual rainfall of less 
than 35 inches. In parts of California it matures on an an- 
nual rainfall of less than 10 inches, although spring barley 
should have about 10 inches of rain during the three months 
of growth. For brewing purposes, barley must be raised where 
there is little rainfall during the latter part of its growth and 
none while in shock. The crop needs plenty of sunshine and 
should ripen in dry weather without dews. 

337. Critical period of growth. — April, June, and July are 
the critical months for barley. Barley is not an important 
crop in Ohio, but a study covering thirty-eight years shows 
that the best yields are nearly always with a comparatively 
dry June, while wet Junes are almost never accompanied by 
yields much above the normal. 

338. In Wisconsin. — A correlation of the weather with 
the yield of barley in Wisconsin, during the period from 1891 
to 1917, shows the following: 

Rainfall Temperature 

Correlation Probable Correlation Probable 

Month coefficient error coeffi,cient error 

April —0.36 ±0.11- +0.32 ±0.12 

May -1-0.32 ±0.12 —0.05 

June +0.20 ±0.12 —0.55 ±0.09 

BUCKWHEAT 

Buckwheat will mature in a shorter period than any other 
grain crop, ten to twelve weeks being sufficient under favor- 
able conditions. It is, therefore, well adapted to high alti- 
tudes and shof t seasons, but its period of growth must be free 
from frosts as it is very sensitive to cold. Because of its short 
growing season, it is successfully cultivated as far north as 
70 degrees. Its cultivation in the United States is confined 
largely to the northern states east of the Mississippi River. 
The district of chief production is in the Appalachian region 
from West Virginia to New York, with a secondary district 
in Michigan. 

339. Weather and buckwheat. — A cool moist summer 
climate best suits this crop, very little being grown in the 
United States where the summer mean temperature is over 
70° and practically none where it exceeds 75°. 



144 AGRICULTURAL METEOROLOGY 

The seeds will germinate best when the soil temperature 
is about 80°F., although they will germinate when the tem- 
perature is anywhere between 45 and 105. In order to ger- 
minate, the seeds must absorb about one-half their weight of 
water. Considerable heat in the early stages of growth is an 
advantage, but it should be cool and moist during the latter 
part of growth and especially when seeds are forming, The 
plants are very sensitive to high temperature and dry weather 
at blooming time, especially when both day and night are 
hot or when accompanied by hot, drying winds. Hot weather 
with constant rain is also unfavorable. In experiments in 
Russia covering a period of fifteen years, the good years were 
with a comparatively low temperature during the second half 
of the flowering period and the poor yields where the temper- 
ature was relatively high. -It was found there that a drought 
during blossoming caused a large production of straw, but 
of very little grain. By sowing buckwheat before April 25, 
through a long series of years in Russia a type had been pro- 
duced that resists a temperature several degrees below freez- 
ing. 



CORN 

Corn or maize is a sun-loving crop of tropical origin, but 
is so flexible in its requirements and so readily adapts itself 
to its surroundings that it is successfully grown over wide 
climatic ranges. It does not mature, however, anywhere 
north of the 50th parallel of latitude, although it may be 
grown for green fodder in favored localities somewhat far- 
ther north. ^ 

340. Where grown. — The great corn regions of the world 
are areas of continental climate. Except where irrigation is 
practiced, most corn is grown in regions having an annual 
rainfall of over 20 inches and a summer temperature averag- 
ing about 75°. A comparatively small area of the earth's sur- 
face is devoted to the intensive cultivation of this crop as the 
optimum climatic conditions for corn are found in only a few 
regions of the world. Outside of the United States, the im- 
portant corn-producing regions are in Roumania, Hungary, 
Mexico, Argentina, and India. Corn does not thrive in re- 
gions of cool cloudy summers. 



WEATHER AND YIELD OF GRAINS 



145 



341. In the United States. — Corn is preeminently an 
American crop and is grown on three-fourths of all the farms 
of the United States. Every fourth acre, almost, of improved 
land in this country is a corn field. In America ''corn is 
king." This country contributes about 70 per cent of the 
world's total production. The corn acreage as well as its value 
is greater than that of wheat, oats, barley, rye, buckwheat, 
rice, fruits, and nuts combined. The 1910 census shows that 
for each dollar the farmers of the nation received for grains 




Fig. 37. — Where corn is grown in the United States. 

over 50 cents came from corn. Fig. 37 shows two centers of 
greatest production in this country, and makes plain the fact 
that a large percentage (three-fourths) is raised in the Missis- 
sippi Valley. While a large proportion of the total corn crop 
is raised in this comparatively limited area, it is an important 
crop in nearly all the eastern states. 

342. Climatic factors. — The region of most intensive cul- 
ture in this country is within a territory where the mean sum- 
mer temperature is from 70° to 80°; the average daily mini- 
mum temperature in summer is over 58°; the average 
frostless season is over 140 daj^s; has an annual precipitation 
between 25 and 50 inches, and a rainfall of 7 to 8 inches in 
July and August. 



146 



AGRICULTURAL METEOROLOGY 



343. Climatic limits.— The growth of corn in any quan- 
tity is Hniited on the north by the mean summer isotherm of 
66° and by the average summer night temperature of 55°. 
The western hmit of extensive cultivation agrees closel}^ with 
the summer (June, July, and August) rainfall line of 8 inches, 
especially in the Southwest where summer droughts are 
likely to prevail, and where evaporation is hastened by hot 




Fig. 38. Dates when corn planting begins. 

winds. As a result, very little corn is grown along the north- 
ern border of the country or in the West except in the more 
favorable locations. 

344. When planted.— As shown by Fig. 38, the planting 
of corn usually begins in extreme southern Texas the latter 
part of January and this work progresses northward at an 
average rate of thirteen miles a day, reaching the northern 
limits of the country about the middle of May. Planting be- 
comes general in the principal corn states about May 15, and 
is usually completed by June 1. 



WEATh^ER AND YIELD OF GRAINS 



147 



345. Temperature and planting dates. — It is an interest- 
ing phenological fact that the average date of the beginning 
of corn planting agrees closely with the date when the sea- 
sonal rise in the mean daily temperature reaches 55°. If the 
date lines on Fig. 39 are drawn on the beginning of planting 




Fig. 39. — Mean daily temperature when corn planting begins in 
different parts of the United States east of the Rocky Mountains, and 
the dates on which these temperatures are reached. 

chart, the lines of the same dates would almost exactly coin- 
cide all the way from the Gulf to the Lakes. 

346. Com planting and average frost dates. — As the aver- 
age last spring frost date lines also agree closely with the tem- 
perature of 55°, it follows that the average date on which the 
last killing frost in the spring occurs has been found to be the 
best date for begirming of corn planting. The ground becomes 
warm enough l^y that time for the germination of seed and 
the danger of serious frost damage will be over by the time 
the corn comes up. 



148 



AGRICULTURAL METEOROLOGY 



347. When harvested. — The beginning of the corn har- 
vest does not progress so regularly as the beginning of plant- 
ing, partly because of various methods of harvesting the crop 
in different sections. Fig. 40 shows the average date when 
cutting and shocking begins. 

348. Length of the growing season of com. — Taking the 
dates for the beginning of planting and those of cutting and 




Fig. 40. — Dates when the cutting and shocking of corn begins, in an 
average season. 



shocking as a basis, the average length of the growing and ma- 
turing season of corn is obtained. This varies from 150 to 
180 days in the South to 120 to 130 days in the North. In 
the main corn-growing states it varies from 130 to 150 daj^s. 
349. Varieties and length of growing season. — Although 
a tropical plant, corn will adapt itself to the climatic require- 
ments so that different varieties have developed that will 
mature in the possible growing season even beyond the 47th 



WEATHER AND YIELD OF GRAINS 149 

degree of latitude. That this is not a recent development is 
shown by the fact that corn was being successfully grown by 
the Mandan tribe of Indians in the Missouri Valley in North 
Dakota when first visited by the whites as early as 1738, and 
had apparently been so cultivated extensively for several cen- 
turies at least. They were growing varieties that matured in 
70 to 90 days. 

350. Temperature and corn. — Corn will germinate in 
three to four days at a temperature of 62°. The length of 
time necessary for germination increases as the temperature 
lowers until the minimum temperature for possible germina- 
tion is reached. In some experiments in New York, one va- 
riety of corn required 430 hours and another 460 hours to 
germinate at temperatures between 37° and 42°. In a test 
by Haberlandt,^ eleven days was required at a soil tempera- 
ture of 51° for the sprouts to show, while only three days were 
necessary when the soil temperature was 65°. In De Can- 
dolle's experiments corn germinated in ten to twelve days at 
temperatures of about 49°, but in less than two days at tem- 
peratures from 70° to 84°. The optimum temperature for 
germination is given as 91° to 93°, and the maximum beyond 
which germination will not take place as slightly above 115^. 

351. Growth and temperature. — Lehenbauer determined 
from experiments that corn seedlings in practical darkness 
and a constant relative humidity of 95 per cent, made almost 
no perceptible growth when the temperature was 40° F. 
(4.5° C), the most rapid growth was at 89.6° F. (32° C.) and 
that the growth ceased at 118.4° F. (48° C). (See Fig. 19). 
His experiments showed that the rate of growth doubled with 
each increase in temperature of about 18° F. from the mini- 
mum to the optimum temperature and decreased in about the 
same proportion from the optimum to the maximum temper- 
ature. The rate of growth w^as practically the same at 116° 
as at 40° while at 88° it was 122 times as great. The rate of 
growth at the different temperatures varied with the length 
of time exposed, which at the figure cited was twelve hours. 
The experiment is valuable only as an indication, as corn 
plants in the field are never subjected to the conditions im- 
posed on the seedlings in the experiment. 

1 111. Agr. Exp. Sta. Bull. 208. 



150 AGRICULTURAL METEOROLOGY 

352. Moisture and corn. — The corn plant is made mostly 
from water and air, with food taken in solution from the soil 
by the roots, and carbon taken from the air by the blades. 
The plant makes the grain by the aid of the sun. The heat, 
moisture, and sunshine must be properly balanced to produce 
the best results. 

353. Transpiration and leaf area. — The amount of water 
transpired from a given leaf area of corn (based on expanse 
of leaf rather than both surfaces) has been found to be about 
one-third as great as the evaporation from a free water sur- 
face of the same area. In hot dry weather, the rolling of the 
leaves reduces the transpiration rate. 

354. The moisture requirements of com vary at different 
periods of growth and with plants of various sizes. Young 
and small plants do not require as much moisture as larger 
and older ones. The amount of water used each week of 
growth gradually increases until the maximum leaf area has 
been developed. This brings the maximum water require- 
ment of corn when it is tasseling and earing. The require- 
ment continues high for four or five weeks, then falls off rather 
rapidly until ripening takes place. 

355. Best dates for planting corn. — Wherever the length 
of the growing season will allow for varying the date of plant- 
ing, it is important to have the corn reach the tasseling and 
ear-forming period when a large amount of rain usually falls 
and when the temperature is relatively high. If the crop is 
irrigated, it should be given the maximum amount of water 
at this time. When the plant is tasseling, it has received prac- 
tically all of its growth. It builds frame-work and constructs 
cells which will be filled with food matter later. 

356. Measurements of water requirements vary, as in- 
vestigators have used different methods of determination and 
under varied environments. Briggs and Shantz determined 
that corn requires an average of 368 pounds of water for every 
pound of dry matter produced. (See par. 201.) Taking into 
consideration the water lost by evaporation, it is calculated 
that the water requirement for each pound of dry matter, 
under average field conditions, will be at least 500 pounds. 

357. The amount of dry matter in the stalks and leaves 
is about the same as in the grain. Hence 112 times 500 or 
56,000 pounds (28 tons) of water will be required to produce 



WEATHER AND YIELD OF GRAINS 151 

each bushel of corn. A 50-bushel crop of corn then requires 
1,400 tons of water. As one inch of water over an acre of 
ground weighs 113 tons, it will require theoretically 12.39 
inches of rainfall to produce a crop of 50 bushels to the acre, 
on an average. The run-off is probably one-third of the rain- 
fall in an average season, so that something like 18 inches of 
rain would be required for a 50-bushel crop. 

358. Seasonal rainfall.— A study of rainfall charts shows 
that the actual rainfall from planting to harvesting of corn 
is greater than this in the southern states, but considerably 
less in the North. . ^ „ . , 

359. Rainfall and the yield of corn.— Rainfall is the most 
important weather factor in varying the yield of corn in the 
corn-belt district of the United States. The critical period 
when rain is most essential is from the middle of July to the 
middle of August; the most important calendar month, how- 
ever, is July. . 

360. July rainfall and com yield.— Fig. 41 shows the 
relation between the rainfall for the month of July and the 
yield of corn over the states of Ohio, Indiana, Illinois, Iowa, 
Nebraska, Kansas, Missouri, and Kentucky for the twenty- 
eight years from 1888 to 1915, inclusive. The averageram- 
fall over these states for July for twenty-eight years is 3.9 
inches. The average yield of corn is 29.7 bushels to the acre. 
The lines show the variation of the rainfall and yield for each 
year from the mean for the whole period averaged for the 
eight states as a whole. For example, in 1889 the aver- 
age rainfall was 1.0 inch above the normal and the yield 
of corn was three bushels to the acre above the normal or 
close to 32 bushels. In 1902 the rainfall was close to 5.0 
inches and the yield averaged nearly 33 bushels or about 4 
bushels to the acre above the normal. 

361. The two curves agree.- The two curves run closely 
together most of the time, although there are some well- 
marked exceptions. This shows that while the rainfall m July 
is an important variant, it is not the controlling factor .^ The 
temperature must be considered, as well as the rainfall m Au- 
gust, and, to some extent in June. An inspection of the dia- 
gram shows that whenever the rainfall for July has been 
above the normal, the yield was above the normal m every 
instance, although in 1896 and 1915 the rainfall was evi- 



152 



AGRICULTURAL METEOROLOGY 



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WEATHER AND YIELD OF GRAINS 153 

dently too great for the best yield. Whenever the rainfall was 
below the normal, the yield has been also below in every year 
except five and in two of these exceptions the rainfall was 
practically normal or only slightly below, and in one other 
the yield was just about normal. 

362. July rainfall and com yield averages. — If the years 
of different rainfall amounts are grouped together, it will be 
found that whenever the rainfall has been one-half inch or 
more above the normal, the yield of corn has averaged 10 
bushels to the acre more than when the rainfall has been one- 
half inch or more below the normal. Taking into considera- 
tion the average acreage devoted to corn in these states and 
the average yield in bushels to the acre for the past ten years, 
it will be found that this average of 10 bushels to the acre 
means a definite increase in the corn crop over the eight states 
of something like 500,000,000 bushels, with this variation in 
rainfall. When corn is worth $1.00 a bushel, this increase in 
the corn yield wijl increase the purchasing power of the farms 
in the central part of the United States fully $500,000,000 
through corn alone. 

363. The four greatest corn states. — It is stated that, of 
the total acreage of corn in the United States, 30 per cent is 
grown in the four states of Indiana, Illinois, Iowa, and Mis- 
souri. Of the total amount shipped out of the county in 
which it is grown, 60 per cent is raised in these four states. 
The average yield of corn is 32 bushels to the acre, and the 
average rainfall for July is 3.9 inches. Fig 42 shows the rela- 
tion between the rainfall over the four states for the month of 
July, as compared with the yield of corn in bushels to the 
acre, over the same area. 

The years are shown at the top of the diagram and run from 
iteS to 1915, inclusive. The lines show the variation of the 
rainfall and yield for each year, averaged for the four states 
as a whole, from the mean for the entire period. While the 
two curves are fairly uniform, there are some variations which 
show plainly that other weather factors besides the rainfall 
for the month of July must be taken into account in consider- 
ing the effect of the weather on the yield of corn in these states. 

364. Comparisons close. — However, when the rainfall has 
been above the normal, the yield has been above the normal 
in every year but two. This shows a probability of the yield 



154 



AGRICULTURAL METEOROLOGY 



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WEATHER AND YIELD OF GRAINS 155 

of corn being above normal 85 per cent of the time when the 
rainfall in July is greater than the average. An inspection 
of the curves shows also that in only four of the years when 
the rainfall was below the normal was the yield greater than 
the average. This makes a probability of 73 per cent that 
the yield of corn will be below normal if the rainfall for the 
month of July is below the average. 

365. Striking averages. — A complete analysis of the rain- 
fall and yield data in these states shows that the average in- 
crease in the yield of corn with each increase of one-half inch 
in the rainfall in July amounts to 2 bushels to the acre, or a 
total increase in the corn yield of 60,000,000 bushels. When 
the rainfall for July in these four states has been between 2 
and 2.5 inches, the yield of corn has averaged 23 bushels to 
the acre, and when the rainfall has been between 2.5 and 3 
inches the yield has averaged 33 bushels to the acre. This is 
an increase of 10 bushels to the acre with an increase of only 
one-half inch of rain at the critical rainfall stage. This in- 
crease amounts to the enormous quantity of 300,000,000 
bushels, worth something like $300,000,000. This also means 
an increase in the value of the corn crop of SIO an acre when 
corn is worth SI. 00 a bushel. 

366. Rainfall and temperature, and corn yield. — Fig. 43 
shows by means of a dot chart the combined effect of the July 
rainfall and temperature on the yield of corn in Ohio during the 
period from 1854 to 1915, inclusive. In the chart, the hea^^ 
horizontal line represents the normal temperature for Ohio 
for the month of July, which is 74°. The figures at the left 
mark lines which represent the variation of the temperature 
above or below the normal as indicated b}^ the prefixes plus 
or minus. The heavy perpendicular line indicates the normal 
rainfall for the state for July, and is close to 4 inches. At the 
top the figures indicate the variation of the rainfall above or 
below the normal. The plus and minus signs in the diagram 
indicate yields of corn above or below the normal, respec- 
tively. . 

The dot chart is made by placing a yield mark for any year 
at a spot on the chart where lines showing temperature and 
rainfall departures from the normal for that year will inter- 
sect if drawn across the chart; for example, in 1866 the tem- 
perature for July averaged 2° a day above the normal while 



156 



AGRICULTURAL METEOROLOGY 



the rainfall was one inch greater than the normal. The corn 
jdeld dot will therefore be placed at the intersection of the 
lines representing these values and as the yield for that year 
was greater than the average, the plus mark was placed at 
this point. The amount of the variation of the yield from 
the normal is not indicated. 

If, in making a diagram of this kind, the plus and minus 
signs are scattered promiscuously over the chart, it will show 
that there is no relation between the weather conditions and 





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Fig. 43. — Effect of July rainfall and temperature on the yield of 
corn, Ohio, 1854-1915. 

the yield. If, however, there is a grouping of like signs on one 
side or in one quarter of the diagram, then a relation is shown. 
367. Wet weather important. — In this diagram, it will 
be seen clearly that there is a decided grouping of the plus 
marks to the right or on the "wet" side of the normal rain- 
fall line, and of the signs to indicate the yield below the nor- 
mal on the left or "dry" side of the rainfall normal. If only 
those years are considered when the rainfall departed one 
inch or more from the normal, it will be seen that when it was 
wet the corn jdeld was above the normal thirteen times, and 
below only once. This indicates that when the rainfall in 



WEATHER AND YIELD OF GRAINS 157 

Ohio for July is one inch or more greater than the normal, the 
probability of a good corn crop is 93 per cent. On the other 
hand, when the rainfall was one inch less than the normal the 
yield was above the normal three times and below thirteen 
times. This indicates a probability of a good corn yield of 
only 19 per cent when the rainfall in July is 3 inches or less. 

368. Rainfall and corn yield averages. — If all the years 
when the rainfall for July in Ohio has been less than 3 inches 
be grouped together, it will be found that the yield of corn 
averaged 30.3 bushels to the acre, and when the rainfall has 
been 5 inches or more the yield has averaged 38.1 bushels to 
the acre. This difference of 7.8 bushels an acre means a va- 
riation of 27,300,000 bushels of corn for the state, worth 
nearly $8 an acre or over $27,000,000, depending on whether 
the state has had an average rainfall of 3 inches or less in July 
or whether the fall has been 5 inches or more. 

369. Temperature effect not so important. — The effect of 
a difference in the mean temperature in July in Ohio in vary- 
ing the yield of corn is not so well marked, as is shown by the 
fact that there is an irregular grouping of the plus and minus 
signs above and below the normal temperature line in Fig. 43. 

370. Combined rainfall and temperature effect. — The 
combined effect of these two weather factors is shown by the 
grouping of like signs in the different quadrants of Fig. 43. 
For example, in the upper right-hand quadrant, which would 
indicate a wet and warm July, there are eleven plus signs and 
only two minus signs. This indicates that when July in Ohio 
is warm and wet, the probability of the corn yield being 
greater than average is 85 per cent. When it is cool and wet, 
the probability of a good corn yield is 73 per cent. On the 
other hand, when July is cool and dry, the probability of a 
good corn yield is only 38 per cent, and when July is warm 
and dry it is only 33 per cent. 

371. Average July rainfall and corn yields in Ohio. — In 
this state, with each increase of one-fourth inch in the rain- 
fall in the month of July, the average increase in the yield 
of corn will be close to 1 bushel an acre ; and between 2 and 4 
inches the average increase in the yield with each increase of 
one-fourth inch in the rainfall will amount to 1 3/2 bushels to 
the acre, the value of which will be almost $6,000,000. A 
further combination of the figures will give the results that 



158 AGRICULTURAL METEOROLOGY 

each increase in the rainfall in July of one-half inch will cause 
an average increase in the corn yield in Ohio of 4,200,000 
bushels, and when the rainfall in,July passes the 3-inch mark 
the increase in the corn crop with an increase in the rainfall of 
only one-half inch will, on the average, amount to 15,050,000 
bushels, valued at over $15,000,000 when corn is worth $1.00 
a bushel. 

372. Correlation for shorter periods than months. — The 
rainfall in the preceding correlations and discussions was for 
complete months, so the next step seems to be the tabulation 
of the rainfall into shorter periods to try and determine the 
exact time during which rainfall has its greatest effect on the 
corn yield. Therefore, the average yield of corn for the three 
counties of Franklin, Madison, and Pickaway, in central Ohio, 
has been calculated and the average rainfall for eighteen coop- 
erative stations in and around these counties. The period 
covered was from 1891 to 1910, inclusive, and it is believed 
that a correlation with the averages obtained in this manner 
has a high degree of accuracy. The correlation was made for 
each ten, twenty, thirty, forty, and fifty days, as shown by 
the following tables: 

Table 12. — Relation Between Rainfall and Yield of Corn in 
Central Ohio for 10-day Periods, 1891 to 1910 
Correlation 
Periods coefficient 

r 

June 1 to 10 —0.09. 

June 11 to 20 +0. 12. 

June 21 to 30 —0.04. 

July 1 to 10 +0.16. 

July 11 to 20 +0.36. 

July 21 to 31 +0.36. 

August 1 to 10 +0.52. 

August 11 to 20 +0.29. 

August 21 to 31 —0.06. 

373. August 1 to 10 most important. — This table seems 
to show plainly that the ten-day period from August 1 to 10 
has the greatest influence on the yield of corn in central Ohio. 
The probable error for that correlation coefficient is =1=0.11, 
which is fairly low. 



n,t Probable error 











±0. 


13 


. . . ±0. 


13 


; ±0. 


11 


.... =^0. 


14 







WEATHER AND YIELD OF GRAINS 159 

Table 13. — Relation Between Rainfall and Yield of Corn in 
Central Ohio for 20-day Periods, 1891 to 1910 
Correlation 
Periods coefficient Probable error 

r 

June 1 to 20 +0.03 

June 11 to 30 —0.10 

June 21 to July 10 +0.07 — 

July 1 to 20 +0.36 ±0.13 

July 11 to 31 +0.41 ±0.13 

July 21 to August 10 +0.50 ±0.11 

August 1 to 20 +0.45 ±0.11 

August 11 to 31 +0.20 ±0.15 

The highest value of r in this table is +0.50 from July 21 
to August 10, and this is about five times the probable 
error. 

Table 14. — Relation Between Rainfall and Yield of Corn in 
Central Ohio for 30-day Periods, 1891 to 1910 

Correlation 
Periods coefficient Probable error 



June 1 to 30 —0.02 

June 11 to July 10 +0. 11 

June 21 to July 20 +0.26 ±0.14 

July 1 to 31 +0.43 ±0.13 

July 11 to August 10 +0.49 ±0. 11 

July 21 to August 20 +0.48 =^0. 11 

August 1 to 31 +0.37 ±0. 13 

374. Thirty days from July 11 to August 10 most impor- 
tant. — Here the greatest coefficient is for the period July 11 
to August 10, when r is +0.49, and the probable error is 
±0.11. These last three tables seem to show that the rain- 
fall before July 10 does not have a very great effect in 
varying the yield of corn. Also that the variations in the 
rainfall after August 31 need not be taken very seriously into 
account. The tables show further that the congelation co- 
efficient for the ten days of August 1 to 10 is higher than 
for any twenty- or thirty -day period, although the difference 
is slight. 



160 AGRICULTURAL METEOROLOGY 

Table 15. — Relation Between Rainfall and the Yield of Corn 
IN Central Ohio for 40-day Periods, 1891 to 1910 

Correlation 
Periods coefficient Probable error 

r 

June 1 to July 10 +0.07 ^_ 

June 11 to July 20 +0.24 • 

June 21 to July 31 +0.36 ±0.13 

July 1 to August 10 +0.53 ±0.11 

July 11 to August 20 +0.60 ±0.10 

July 21 to August 31 +0.52 ±0.11 

There seems little question in this table of the dominating 
influence of the rainfall during the period from July 1 1 to Au- 
gust 20. This correlation coefficient of +0.60 is six times the 
probable error. 



Table 16. — Relation Between Rainfall and the Yield op Corn 
in Central Ohio for 50-day Periods, 1891 to 1910 

Correlation 
Periods coefficient Probable error 

r 

June 1 to July 20 +0. 17 

June 11 to July 31 +0.36 ±0.13 

June 21 to August 10 +0.49 ±0.11 

July 1 to August 20 +0 . 59 ±0 . 10 

July 11 to August 31 +0.55 ±0.10 

The correlation coefficient from July 1 to August 20 in this 
table is +0.59 and is slightly less than six times the probable 
error. 

It is believed that the district covered by the yield and rain- 
fall figures in Tables 11 to 16 makes them very reliable 
and that the values may be taken as a standard for this sec- 
tion of the country. Similar tables should be worked out for 
other districts, however, as the correlations might vary under 
different distribution of rainfall or different temperature and 
sunshine. 

375. Weather effects during different periods of develop- 
ment. — After showing the relation between the corn yield 



WEATHER AND YIELD OF GRAINS 161 

and a single element, the rainfall, during certain definite pe- 
riods, the question naturally arises as to what is the effect of 
all the elements, i. e., the "weather," during different periods 
of development of the corn plant. This can be answered by 
a study of certain data that have been compiled at Wauseon, 
Fulton County, Ohio. 

In Table 17 there have been entered certain important 
data relating to corn growth and development from 1883 to 
1912 as taken from the records of Mikesell. As will be seen, 
they cover the dates planted, dates that plants appear above 
ground, dates in blossom, and the dates ripe, together with a 
statement of the quantity and quality of the crop. From 
1883 to 1901 the dates are for operations on his own farm, and 
during the balance of the period for certain nearby fields, the 
same field being used for the entire season. The average dates 
and periods of development are given at the bottom of the 
table. 

376. Thermal and rainfall constants at Wauseon, Ohio.— 
Thermal and rainfall constants have been worked out for the 
different stages of growth of corn at Wauseon, Ohio, for 1883 
to 1912, and appear in Table 18. In addition, the amount 
of available heat and the rainfall for ten days before the date 
of planting was determined and appears in the table. 

This table should be studied in connection with the data 
in Table 17 for the dates of planting, blossoming, and so 
on, and the number of days between these dates during dif- 
ferent years. 

377. The average date for planting com is May 14, and 
the average number of diiys for the plants to appear above 
the ground is nine. Table 18 shows that the average to- 
tal number of thermal constant degrees during this period has 
been 143°, and the average rainfall 1 inch. The average time 
from the date the plants appear above the ground until they 
are in blossom is sixty-two days, and the thermal constant 
averages 1,599°; the rainfall averages 7.4 inches. The aver- 
age date when the corn is in blossom at Wauseon is July 25, 
although this date has varied between July 10 and August 6. 
The average date when the corn has ripened is September 13; 
or fifty days after the tihie of blossoming. The average ther- 
mal constant during this time is 1,337°, and the average rain- 
fall 4.6 inches. 



Table 17. — Phenological Dates and Data for Growth of Corn 
AT Wauseon, Ohio, 1883 to 1912, by Thomas Mikesell 

(Lat., 41° 35' N.; Long., 84° 07' E.; alt. 780 ft., A. M. 8. L.) 









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July 26 


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June 23 


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44 




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10 


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42 






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17 


10 


25 


69 




10 


47 


80 


Good 


1905 


9 


15 


6 


18 


64 


Aug. 


30 


43 


75 


Good 


1906 


10 


16 


6 


17 


62 


Sept. 


10 


55 


80 


Good 


1907 


April 26 


6 


10 


30 


85 




3 


35 


75 


Good 


1908 


May 21 


28 


7 


30 


63 




15 


47 


80 


Good 


1909 


14 


21 


7 


Aug. 6 


77 




25 


50 


80 


Good 


1910 


11 


21 


10 


1 


72 




30 


60 


90 


Fair 


1911 


10 


17 


7 


July 20 


64 




8 


50 


80 


Fair 


1912 


10 


20 


10 


22 


63 




2 


42 


95 


Good 


Aver. 


May 14 


May 23 


9 


July 25 


62 


Sept. 


13 


50 


76 





1 Data for the years 1883 to 1901, inclusive, apply to Mikesell's own 
estate; data for 1902 to 1912 apply to certain nearby fields, the same 
field being used for the entire season. 

162 



Table 18. — Thermal Constants (Base 43'' F.) and Rainfall During the 
Growtu of Corn at Wauseon, Fulton Co., Ohio, 1883 to 1912 



Thermal 


Rainfall 


Year 


f 1^ 

op 


1 

■S 

1' 


-2 


C55 




.1 i' 

II 


••Si 

i 


1 

o 




o 


•S 'i 

^ 1 

II 


if 
tl 


1 

o 

1 




-F 


°F 


°F 


°F 


0^ 


In 


In 


In 


In 


In 


In 


In 


1883 


139 


141 


1,583 


1,264 


270 


290 


0.6 


2.7 


13.7 


6.1 


0.7 


3.7 


0.0 


1884 


114 


161 


1,496 


1,412 


240 


290 


1.0 


0.8 


6.0 


5.9 


1.1 


0.0 


4.5 


1885 


114 


147 


1,520 


1,432 


330 


340 


0.1 


1.6 


6.6 


8.4 


1.8 


0.2 


2.6 


1886 


134 


128 


1,477 


1,565 


290 


260 


0.9 


0.9 


2.8 


5.5 


T 


T 


0.2 


1887 


205 


131 


1,693 


1,371 


350 


330 


0.1 


1.4 


8.4 


1.9 


1.0 


1.0 


0.0 


1888 


128 


110 


1,600 


1,410 


270 


320 


1.4 


0.4 


5.6 


2.7 


0.1 


0.1 


0.4 


1889 


250 


143 


1,649 


1,239 


250 


240 


1.3 


0.4 


15.3 


2.3 


1.0 


1.6 


0.9 


1890 


167 


131 


1,365 


1,330 


270 


360 


1.1 


T 


4.4 


6.3 


T 


T 


T 


1891 


103 


148 


1,568 


1,366 


200 


250 


0.4 


0.6 


6.6 


4.0 


0.4 


0.4 


0.4 


1892 


318 


165 


1,253 


1,238 


310 


310 


1.0 


1.2 


5.3 


6.2 


0.3 


1.2 


T 


1893 


140 


163 


1,634 


1,411 


300 


300 


1.0 


0.3 


8.4 


1.4 


0.4 


1.0 


0.4 


1894 


139 


161 


1,638 


1,300 


290 


330 


0.9 


1.3 


5.3 


1.1 


0.2 


T 


0.2 


1895 


157 


175 


1,919 


1,428 


250 


270 


T 


1.2 


2.3 


3.8 


0.7 


0.2 


0.5 


1896 


235 


154 


1,443 


1,490 


280 


290 


0.2 


0.6 


8.2 


13.8 


4.0 


1.4 


6.4 


1897 


153 


186 


1,232 


1,486 


290 


320 


1.0 


1.2 


5.4 


3.5 


1.0 


1.7 


1.3 


1898 


150 


177 


1,566 


1,25C 




. . . 


1.7 


1.4 


6.1 


4.7 




. . . 




1899 


109 


154 


1,478 


1,344 


290 


320 


1.4 


1.2 


4.7 


2.3 


2^8 


2.2 


i!2 


1900 




























1901 


151 


201 


1,468 


1,54G 




... 


o's 


1.8 


8.3 


'2'2 


. 




. . . 


1902 




























1903 




























1904 


146 


109 


1,637 


1,140 


290 


270 


0.1 


o'o 


6.5 


'3^6 


0'8 


L6 


0^6 


1905 


142 


97 


1,526 


1,210 


290 


270 


0.8 


3.3 


10.2 


2.9 


0.1 


0.1 


0.2 


1906 


91 


127 


1,574 


1,607 


300 


280 


0.6 


0.4 


6.8 


6.1 


0.3 


2.3 


0.2 


1907 


-25 


36 


1,702 


897 


290 


160 


0.4 


0.8 


10.7 


3.3 


1.4 


1.3 


2.0 


1908 


213 


199 


1,735 


1,229 


300 


300 


2.6 


0.4 


9.6 


3.4 


0.0 


2.1 


0.2 


1909 


135 


107 


1,984 


1,223 


310 


300 


2.5 


0.4 


10.7 


6.0 


0.5 


1.1 


2.6 


1910 


78 


114 


1,811 


1,453 


290 


260 


1.0 


0.7 


6.6 


6.9 


0.1 


3.4 


T 


1911 


125 


166 


1,913 


1,322 


290 


230 


0.1 


T 


10.2 


5.0 


1.1 


1.0 


0.8 


1912 


168 


123 


1,645 


1,107 


300 


270 


0.8 


2.2 


5.3 


5.1 


0.6 


0.8 


0.8 


Means 


150 


143 


1,599 


!,337 


296 


286 


0.9 


1.0 


7.4 


4.6 


0.8 


1.1 


1.1 



163 



164 AGRICULTURAL METEOROLOGY 

Table 18 also gives the thermal and rainfall constants 
for ten days before blossoming and for ten days after blossom- 
ing, as well as the rainfall during the ten-day period from five 
days before to five days after blossoming. 

378. Thermal constants and corn yield, Wauseon, Ohio. 
— In Table 19, the correlation coefficient has been given 
between the thermal constants during different periods of 
corn development and the percentage of a good crop, as re- 
ported by Mikesell. It is unfortunate that we do not have 
the yield of corn in bushels to the acre, yet believe that the 
percentage figures have been carefully considered by the ob-. 
server. 



Table 19. — Results of Correla.tion Between Thermal Constants 
AND Corn Yield, Wauseon, Ohio, 1883 to 1912 

Correlation Probable 

Periods coefficient error 

r 

(1) For 10 days before planting — . 03 

(2) From date of planting to date dt»ove 

ground —0.03 ■ 

(3) From date above ground to date of blos- 

soming +0.18 ±0.12 

(4) From date of blossoming to date ripe . . . +0 . 08 

(5) Daily mean temperature for 10 days be- 

fore blossoming — . 003 — 

(6) Daily mean temperature for 10 days after 

blossoming .' —0.28 ±0.10 

There is a slight positive relation between the temperature 
from the date when the corn appears above the ground and 
the date of blossoming and the yield of corn, as well as a 
negative relation between the temperature for ten days after 
blossoming and the yield, but these correlation coefficients 
are all too low to be given any consideration. This table seems 
to show that there is little or no relation between the daily 
mean temperature and the yield of corn. 

379. Rainfall constants and corn yield, Wauseon, Ohio. — 
In Table 20 the correlation coefficients between the yield 
of corn and the rainfall during the different periods of growth 
are shown. 



WEATHER AND YIELD OF GRAINS 165 

Table 20. — Rerults of Correlation Between Rainfall and Corn 
Yield, Wauseon, Ohio, 1883 to 1912 

Correlation Probable 

Correlation factors coefficient error 

r 

(1) For 10 (lays before planting +0.01 

(2) From date of planting to date above 

ground — . 06 

(3) From date above ground to date of blos- 

soming — . 03 — ■ ■ 

(4) From date of blossoming to date ripe. . . +0.29 ±0.11 

(5) From 5 days before blossoming to 5 days 

after blossoming +0.45 ±0. 10 

(6) For 10 days before blossoming +0 . 20 

(7) For 10 days after blossoming +0.74 =±=0.05 

(8) For 20 days after blos.soming +0 . 57 ±0 . 08 

(9) For 30 days after blossoming +0.46 ±0.09 

The results from this table are very important. It seems 
to make plain that there is no relation between the variations 
in rainfall in the first part of the period of growth of the corn 
crop and the variations in the yield. The average date of 
blossoming as determined in Table 17, is July 25, or sixty- 
two days after the plants appear above the ground and 
seventy-one days after planting. The correlation coefficient 
for the first three items in Table 20 is much too near zero 
to receive consideration. The correlation coefficient in item 
4 indicating the effect of the rainfall between the dates of 
blossoming and ripening is +0.29, but as this is only two and 
one-half times the probable error, even this is not very close. 

380. Rainfall near the blossoming time important. — The 
value of the coefficient for the rainfall for ten days before the 
date of blossoming as stated in item 6 is also too low to be 
given serious consideration. In item 5, however, covering 
the time from five days before blossoming to five days after 
blossoming, the correlation coefficient is four times the prob- 
able error and a relation is apparently esta])lished. 

It is in item 7, however, that there is the highest correla- 
tion coefficient. This shows that the rainfall for the ten days 
after blossoming has the greatest effect on the yield of corn 
of any period in the development of the plant. This value 
is +0.74, and it is fifteen times the probable error. This coef- 

\ 



166 AGRICULTURAL METEOROLOGY 

ficient is considerably higher than even that for the twenty 
or thirty days following the date of blossoming. In Tables 
12 and 16, there were given ,the correlation coefficients 
for the rainfall for the state of Ohio as a whole, compared 
with the yield of corn, for arbitrary ten-, twenty-, and thirty- 
day periods. All near the average date of blossoming gave 
high values. These facts combined with the high value in 
item 7 of Table 20 go to show that the rainfall immediately 
after blossoming has a very dominating effect on the yield of 
corn. 

381. Combined, effect of rainfall and temperature. — 
Item 7 in Table 20 indicates a direct relation between the 
rainfall for ten days after blossoming and the yield of corn, 
and item 6 in Table 19 seems to show an opposite effect of 
the temperature on the yield during the same period. 

382. Effective rainfalls. — It is well known that small 
rainfalls during a drought may actually do more harm to a 
crop than good, because by merely wetting the surface of the 
ground an effective dust mulch may be destroyed and thus 
more water be lost to the crop by evaporation than has been 
gained by the shower. Or numerous light showers during the 
early growth of the corn, by merely wetting the surface may 
cause the plants to root near the surface where the soil will 
quickly dry out in later dry spells. In investigations of ac- 
cumulative effects of weather, it was found that when July 
was quite dry the final yield was greater if the previous June 
was moderately dry also. The rate of growth and develop- 
ment of corn plants have been determined with certain defi- 
nite amounts of water in the laboratory. But to try to answer 
the often repeated question as to just what rainfall amounts 
are actually beneficial or are most beneficial to the growing 
corn, the following plan has been adopted: The rainfall for 
a definite district and period is multiplied by the total number 
of days with a certain amount of rain, and divided by the 
whole number of days in the period. The equation is simple; 

— , where a is the total rainfall for the period, b the number 

of days with 0.10 inch, 0.20, 0.30 inch, and so on, rainfall or 
more, and c the total number of days in the period. 

In Table 21 the effective rainfall was determined by tak- 
ing the rainfall at Columbus, Ohio, for the fifty-one day pe- 



WEATHER AND YIELD OF GRAINS 167 

viod from June twenty-one to August ten for twenty years, 
working out new factors in accordance with the formula as 
above, and correlating these new factors with the yield of 
corn in Franklin County, Ohio. 

This method shows whether a certain amount of rain is as 
effective coming in many small showers, as it is in a few heavy 
showers and it is accomplished by eliminating consideration 
of days with rainfalls below 0.25 inch. 

The general rule has been stated that for equal quantities 
of rain its value to agriculture increases as the number of 
rainy days diminishes, and on the other hand diminishes as 
the number of rainy days increases. This can be true, how- 
ever, only up to a certain point. 

Table 21. — Correlation Table for Determining the most Effec- 
tive Rainfall in the Yield of Corn in Columbus and Franklin 
County, Ohio 

Corrdnlion Prohable 

Correlation factor coefficient error 

r 

Kainfall for July and yield of com +0 . 48 ±0.11 

Rainfall, June 21 to August 10, and yield of 

com +0.G0 ±0.10 

Factor determined for the amounts given 
below as per formula and the yield of com 

Days with 0.01" or more +0 . 61 ±0 . 10 

'' +0.61 ±0.10 

" +0.61 ±0.10 

'' +0.64 ±0.09 

" +0.59 ±0.10 

" +0.61 ±0.10 

" +0.70 ±0.08 

" +0.55 ±0.10 

" +0.56 ±0.10 

'' +0.57 ±0.10 

" +0.38 ±0.13 

'' +0.59 ±0.10 

" +0.41 ±0.12 



(( tc 


0.10" 


a u 


0.20" 


CC i( 


0.25" 


(( (( 


0.30" 


(( (C 


0.40" 


(( le 


0.50" 


" " 


0.60" 


a (( 


0.70" 


u u 


0.75" 


a t( 


0.80" 


CC CC 


0.90" 


CC CC 


1.00" 



383. Rainfalls of 0.50 inch or more most effective. — This 
table indicates that rainfalls of 0.50 inch or more are the most 
effective in determining the yield. For fear that the results 
might be affected by taking the rainfall at only one station, 



168 



AGRICULTURAL METEOROLOGY 



similar correlations have been calculated for the yields in 
Franklin, Madison, and Pickaway counties, in central Ohio, 
and for the rainfall at all of the stations in and around those 
counties, eighteen in all, for the period from July 21 to August 
10. The results follow in Table 22. 

Table 22. — Results from Correlations for most Effective 
Rainfalls, Central Ohio, 1891 to 1910 

Correlation Probable 

Rainfall factors coefficient error 

r 
Rainfall, July 21 to August 10, and corn 



yield. 



+0.50 ±0.11 



Factor determined for the amounts below as 

per formula and the yield of corn 
Days with 0.01" or more +0.44 ±0 12 

U U Q_JQ// U U 



0.20" " 

0.25" '' 

0.30" " 

0.40" " 

0.50" '' 



+0.51 ±0.11 

+0.43 ±0.13 

+0.49 ±0.11 

+0.50 ±0.11 

+0.47 ±0.11 

+0.G4 ±0.09 

The differences in the correlation coefficients for the lower 
rainfall amounts are not great and could be purely accidental. 
But the higher value of r for 0.50 inch or more corresponds to 

/^Af /ff^ J396 /897 /S3am9 /900 /90/ /90^ 1903 /904 J905 /906 f907 1908 

Bushelt 

































<^' 


\, 




















\ 




( 




\ 


















/ 


\ 




1 




\ 


^4 


W 














/ 


Vs 




1 

1 






'^ / 


\\ 














/ 


\ 


""^v. 


1/ 


% 




/ 


\' 














/ 


\ 




^^ 




X 


/ 


\ 


"^^^ 






^' 




















\ 




\ 


/ 


."'''' 





'' 






^"~- 














\\ 


/ 














Corn Crc 


P 




V 


/ 














^a/nfa// 






\' 


/ 




















1 




\ 


f 












/^.T. 



Fig. 44. — Relation between the July rainfall and the yield of corn in 
Tennessee, 1894-1908. 

that determined in Table 21 and seems to show that one-half 
inch of rain is more beneficial than lesser amounts. 

384. Rainfall and com in Tennessee. — Fig. 44 illustrates 
the relation between the rainfall for July and the yield ot corn 



WEATHER AND YIELD OF GRAINS 



169 



in Tennessee. In this state the corn tassels in July and is 
favorably affected by an abundance of rain as in other sec- 
tions. 

385. The accumulated effect of the weather on the con- 
dition of corn in Iowa and Missouri in 1917 is shown in Fig. 45. 
The spring and early summer of 1917 were cold and wet, 
but on July 1 the condition of the crop as reported by the Bu- 



No. 3. Iowa and Mi 


ssoori. 


■ ^1 llliiiillll 

S 2.6 _s- -^ 


1 1 rr M f f 1 1 r 


1 2.4 

J 2.2 L 

- 2.0 




1 1.8 


, 5 


^ L4 


- Id 


8 1.2 -^, ■ 

0.6 - !^ = **■".. I . . . 


Percentage of e 
tio 


Ji^M 


[a — r.Jr-l-»— }^ 


1 r^TO^m 


80 
75 



Fig. 45. — Diagram showing the effect of the weather on the condition of 
corn in Iowa and Missouri in 1917. 

reau of Crop Estimates of the Department of Agriculture was 
not far from the ten-year average in all of the principal corn- 
growing states. Dry and warm weather the latter part of 
June and most of July lowered the prospect in the western 
Plains region, but in Iowa and Missouri, although drier than 
normal, the lack of moisture was not sufficient to lower the 
condition. 

386. Weather and com, 1918.— Fig. 46 shows that warm 
and wet weather in May and the first of June, 1918, was favor- 
able for corn in Missouri and the condition was well above the 



170 



AGRICULTURAL METEOROLOGY 



ten-year average the first of July. From the week beginning 
July 3 until about the middle of August, however, the precip- 
itation was constantly deficient in Missouri, four of the weeks 
being practically without rain. As a result, together with the 
high temperature in August, there was a marked deterioration 
in the condition of corn through July and August in this state. 



No. 2. Ui830un. 




u 




Vi 


A 2-6 
1 2.4 
1 2.2 
•3 2.0 
g L8 
5 !•' 

h. ^* 
1 " 
1 »•» 

* 0.8 

0.6 

0,4 

0.2 



fi +8° 

1 -t-eo 

1 +20 

1 ^ 

1 -20 

2 - 4" 

1 -^ 
t? -10° 






1 






































fl 






















d 






















8 






















^ 






















S 




















'xU 




■4"¥ 


.. 
















— - 


.. _"^ 


^f 


*^ 






— 




,XII" 








T 




— 




— ' 




itt 


T " fl 




- 


1 






m 


Ej 




lit 


s 


1 


T 




1 


■ 




1 


k 




III 


' £ 


1 


1 


. :i 


I 1 


1 


• 


i 


i 




±t± 


-f- o« 






















120 






j^ ^ 


A> 












Z!^ 


116 




/ 


^-^ 










/- 


^ 


"^^ 


110 




z: 


2 


V 


r 












\ 1 106 




z^ 




V. 


1 


^ 










\ 1 -inn 




r"^ 






^"^ 






A 






\ % 












\/ 










\- s 


^ 


J 


















x S 


N 


TT 
















\ 


80 




SL 
















^ 


75 




















\ 





Fig. 46. — Diagram showing the effect of the weather on the condition 
of corn in Missouri in 1918. The condition of corn on the first of 
each month, as compared with a ten-year average, expressed in 
percentages, is indicated by the dots which are connected by broken 
lines. The significance of the temperature and rainfall values is 
explained under Fig. 34. 



387. Spring frosts and com. — Early planted corn makes 
a slow growth and hence is not so susceptible to frost damage 
as that planted later and which may be growing more rapidly 
when a late frost occurs. Very young corn may be cut by 
frost without serious injury to the plants. 

388. Fall frost damage. — Frost in the fall is seldom early 
enough or covers sufficient territory to cause widespread loss 



WEATHER AND YIELD OF GRAINS 171 

of the corn crop. Even if some fodder is frosted, a light or 
moderate frost may cause more rapid ripening. 

389. Frost in 1917. — In 1917, however, a cold late spring 
and generally cool sunnncr was followed by unusual and 
severe frosts, the first early in September. As a result, no 
corn fully matured in northern North Dakota, Minnesota, 
and Wisconsin, and less than 50 per cent as far south as 
northern Ohio, Indiana, and Illinois, and in northeastern 
Iowa. In an average year, 90 per cent or more matures 
in the southern part of this area, and 50 to 75 per cent in 
that part of the district where none matured in 1917. 

390. Freezing injury to seed corn. — The germ of a sound 
kernel of corn is an embryonic living plant with stalk, leaves, 
and root. When this living germ contains a large amount of 
moisture, some physical or chemical change is brought about 
by freezing which results in death. Corn containing 10 to 14 
per cent of moisture will not be injured by any amount of 
winter cold, but when it contains 60 per cent it may be 
killed by a prolonged exposure to a temperature but slightly 
below freezing. In fact, a very close relation exists between 
the moisture-content of the kernel and the degree of cold re- 
quired to kill the germ. 

391. Damage to seed com in 1917. — Some of the corn 
that was seemingly mature in 1917 was so full of moisture 
that while it showed a fairly high germination in the early 
winter, it was so injured by very cold weather later that the 
germination was greatly reduced. 

392. Short periods of drought and pollination. — Corn has 
two kinds of flowers situated some distance apart and in a 
normal season these will both appear at the proper time for 
fertilization. 

Drought, however, often hastens the shedding of the pollen, 
but delays the appearance of the silk. In this case, the pollen 
is wasted before the silk appears, proper fertilization is pre- 
vented, and no amount of rain later can produce a good crop. 
Cold and wet weather retards or even prevents shedding of 
the pollen. 

393. Temperature and growth. — Corn makes most of its 
growth during the season of highest temperature, and this 
growth is retarded by cool weather or cold nights. It re- 
quires its greatest moisture in the summer when droughts are 



172 AGRICULTURAL METEOROLOGY 

liable to occur, and when rainfall is less effective on account 
of the greater evaporation due to high temperatures. 

394. Drought and. transpiration. — The maximum trans- 
piration in corn is during the warmest part of the day. On 
days of extreme temperature in very dry spells, there may be 
an atmospheric demand of ten pounds of water from a single 
average corn plant during twenty-four hours, the greater part 
in the seven hours in the middle of the day. Such days are 
very critical for corn if there is not a sufficient amount of 
moisture in the soil to meet this demand. It is evident that 
a drought during a brief period may affect the yield more than 
can be overcome by abundant rains at other stages of its 
growth. 

395. Rate of seeding. — When the hills of corn are 33^ 
feet apart, there will be a stand of 10,668 stalks to the acre 
if an average of three kernels to the hill germinate and grow, 
or 14,224 to the acre if four kernels grow in each hill. In field 
practice, it has been found that from 3,630 to 7,260 stalks to 
the acre are all that can be properly supplied with the mois- 
ture that is available in the average year. It is stated that 
the great corn crop raised in South Carolina a few years ago 
was planted at the rate of 30,000 stalks to the acre, and hap- 
pened to receive an abundant rainfall just at the right period 
of its growth. 

396. Weather and com in the South Temperate zone. — 
The following extracts from the "Agricultural Gazette" of 
New South Wales, Vol. XXVI, are of decided interest as they 
substantiate the results of studies in the North Temperate 
zone : 

It is well known that there is a critical stage in the growth of maize 
called the "cobbing stage," during which absence of sufficient moisture 
has a marked effect on yield. It has been determined by considerable 
observation and by statistics that the yield of a maize crop is almost 
directly proportional to the amount of rain received by the crop for 
the three or four weeks following flowering, other factors, of course, 
being equal. 

Hot, blasting winds during flowering are known to have very in- 
jurious effects on fertilization, either scorching up the pollen so that it 
will not germinate, or drying out the silks to such an extent that they 
have not sufficient moisture to germinate the pollen grains. To avoid 
damage by these winds, it has been found advisable in maize growing 



WEATHER AND YIELD OF GRAINS 173 

for grain on the Murrumbidgcc Irrigation Area to plant early varieties, 
either early in September or late in December, so that these crops do 
not tassel during the hotter months of the year — December to Feb- 
ruary, inclusive. 

When the flowering period extends regularly over some weeks, it is 
possible that the crop possesses an adaptability that will enable it to 
weather through a few days' scorching winds more successfully than 
if the flowering period is limited to a few days, as is the case with some 
varieties. 

The value of sunlight is so well known that it calls for little com- 
ment. Many maize growers have recently been allowing greater width 
between the rows, and many have a fancy for running the drills in a 
north and south direction, so that the maximum amount of sunshine 
reaches the plants. It is sufficient here to say that if enough sunlight 
does not reach the plants at the flowering stage, the size of the cobs 
and also their fertilization generally suffers. This is particularly ob- 
served to be the case in a thick stand in a very cloudy season. 

It has been stated by some writers on maize that a crop may be 
"starved for rain" during the early growth, and yet yield excellently 
if it gets sufficient rain during the late growth. It is admitted that 
one of the worst things that can happen to the maize crop is for it to 
get plenty of rain during the early stage and a dry time during the 
later stage, but there is no doubt that the best crops are produced when 
there is a sufficiency of rain throughout the growing period, although 
it is preferable to have a dry period during the early half of growth 
rather than during the later half. In fact, some farmers go so far as to 
say that it does a crop good to get a set-back during the early growth, 
and it may be said that this is desirable when the later growing period 
is unfavorable. 

OATS 

The oat plant is most at home in cool moist climates; it is 
one of the most important grain crops in the North Temper- 
ate zone. 

397. Range in United States. — Oats are widely grown in 
this country, but about four-fifths of the crop is produced in 
an area from western New York westward along the lower 
Lakes to the central Missouri Valley. The centers of most 
intensive cultivation are in northeastern Illinois and north- 
western Iowa, as is shown by Fig^ 47. Spring oats are grown 
in this district. 

398. Seeding and harvesting. — Spring oats are seeded in 
the late winter and very early spring, when the mean daily 
rise in temperature reaches 43° on an average. The crop is 



174 



AGRICULTURAL METEOROLOGY 



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WEATHER AND YIELD OF GRAINS 175 

harvested in the early summer in the south-central and mid- 
summer in the northern states. The period between plant- 
ing and harvesting winter oats is about 210 days. The aver- 
age growing period for spring oats is close to 110 days in the 
northern part of the country and 120 days in the southern 
part. 

399. Winter oats. — In the Gulf and south Atlantic states 
winter oats are best adapted and the crop is seeded in the fall 
and harvested in the late spring. The region of winter-oat 
production in the United States is bounded on the north, ap- 
proximately, by the winter mean isotherm of 35°, which ex- 
tends broadly from Virginia and Kentucky westward across 
southern Missouri and central Oklahoma and then southward 
to the Gulf. Winter oats are less hardy than winter wheat. 
Fall-sown oats usually grow more vigorously and mature from 
ten days to two weeks earlier than those sown in the spring. 
They yield less than spring oats. 

400. Weather and oats in Portage County, Ohio. — This 
county is in northeastern Ohio and produces a large acreage 
of oats. The following table shows the correlation between 
the temperature and rainfall and the yield of oats covering a 
period of fifty-three years. 

Table 23. — Correlation Between Temperature and Rainfall 
AND Yield of Oats in Portage County, Ohio, 1860 to 1913 

Month Rainfall Temperature 

Correlation Probable Correlation Probable 

coefficient error coefficient error 

April -0.12 +0.26 ±0.08 

May —0.14 _ +0.04 - 

June +0.25 ±0.08 -0.30 ±0.08 

July +0.39 ±0.07 -0.04 

While none of these correlations is very high, j^et they show 
plainly that a warm April and a cool and wet June are the 
conditions most favorable for oats. Oats seeding becomes 
general in that region between April 11 and 21 and harvest 
begins during the last decade in July. A more detailed study 
of the data shows that a dry and warm April is decidedly favor- 
able for oats in this county, while June should be cool and wet 
for the best results. When June is warm and dry, the yield 
will be below the normal nearly 80 per cent of the time. 



176 



AGRICULTURAL METEOROLOGY 



As oats are seeded in April in this region, it indicates that 
dry and warm weather produces conditions for a good seed- 
bed and for the work of planting, while a cool wet April ap- 
parently makes conditions unfavorable for planting. 

401. In Wood County, Ohio. — A similar study of weather 
and the yield of oats in Wood County in northwestern Ohio 

covering a period of 
twenty years gave no 
decided correlation for 
any single month. It 
showed, however, that 
when the average tem- 
perature for April and 
May, combined, was 
higher than normal 
the yield was above 
normal with two ex- 
ceptions, one quite 
marked. 

402. For the state 
of Ohio. — As oats are 
grown largely in the 
northern part of the 
state, a correlation of 
the yield with tem- 
perature and rainfall 
for the state as a 
whole, should not be 
expected to give high 
coefficients. The 
highest coefficients 
found, however, are 
for a cool June, while 
a wet June and July 
are the most favorable 
for the crop. 

403. In Indiana. — A moderately wet May is favorable 
for oats in Indiana. In thirty-two years the rainfall in May 
for that state averaged above the normal eighteen times an d 
below the normal fourteen times. In the eighteen years with 
a wet May the oat yield was above the normal twelve times 



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Fig. 48. — Effect of the rainfall and tem- 
perature in June on the yield of oats 
in IHinois, 1878-1915. 



WEATHER AND YIELD OF GRAINS 177 

and below the normal six times. In the fourteen years with 
a deficient rain, the yield of oats was less than normal twelve 
times and above only twice. Cool weather is desirable in 
June in this state for the best yield of oats. 

404. Illinois, 1878 to 1915. — June is also the most im- 
portant month in this state in the effect of weather on the 
yield of oats. Fig. 48 shows that cool and wet Junes have 
been followed by yields above the normal 82 per cent of the 
time, while dry and warm Junes have been followed by good 
yields only 18 per cent. None of the other months shows a 
marked relation. 

405. Iowa. — April is an important ''weather" month for 
oats in Iowa. During the period from 1890 to 1915 when 
April was warm and dry, the yield of oats was above the nor- 
mal 73 per cent of the time and when the month was cool and 
wet the yield was below the normal 71 per cent. As seeding 
becomes general in this state in the first part of April, this in- 
dicates the importance of a good seed-bed. There is some 
evidence that the temperature in June and July should be 
slightly below the normal for the best yield of oats in 
Iowa. 

406. Maryland. — Seed formation of spring oats is pre- 
vented in southeastern Maryland if there is hot humid 
weather at heading time. 

407. North Dakota, 1892-1915.— Oats are seeded in 
North Dakota generally later than about the middle of April 
and are not harvested until August. This later season of crop 
development makes the critical period for oats extend into 
July although June is an important month. During the pe- 
riod from 1892 to 1915 whenever June was warm and dry, the 
yield of oats was below the normal in every instance and when 
cool and wet the yield was above the normal 90 per cent of 
the time. 

The yield of oats in bushels per acre is lower in North 
Dakota than in the upper Mississippi valley and Lake region 
because of the lighter rainfall and the later critical period of 
growth. Hot weather in July may cause blighting and rust 
development. 

408. Wisconsin. — The following shows the correlation 
between the weather and the yield of oats in Wisconsin for 
the period from 1891 to 1917: 



178 AGRICULTURAL METEOROLOGY 

Table 24. — Correlation between Temperature and Rainfall and 
Yield of Oats in Wisconsin, 1891 to 1917 



Month 


Rainfall 
Correlation 


Probable 


Temperature 
Correlation Probable 




coefficient 


error 


coefficient error 


April 
May 
June 


— 0.31 

+0.23 
+0.12 


=t0.12 
±0.12 


+0.39 ±0.11 
1 ond 


-0.47 ±0.10 



409. Critical period for oats. — Notwithstanding the fact 
that oats are a cool weather crop and that spring oats should 
be seeded as early as practicable, the facts given above show 
that the temperature should be above the normal for the sea- 
son and locality and the precipitation below the normal to 
produce the best conditions for seeding and the germination 
of the grain. 

While the heads are forming, however, and the grain being 
developed, the crop must have cool and moderately wet 
weather to produce the best yields. Cool weather favors the 
ripening of the grain, while the crop is often materially re- 
duced by a few hot days when it is near maturity. 

410. Weather and. oats in Russia. — Brounoff found that 
the critical period of oats in respect to moisture is within the 
ten-day period before heading. Oats were seeded in his in- 
vestigations early in April, headed the last of June, and were 
harvested the last of July. An abundance of moisture was 
found necessary in June when the plants ''are ready to de- 
velop a great number of new important vegetative organs." 

He found further that cold weather and morning frosts 
from the time of seeding up to the appearance of tillers were 
not seriously damaging, but contribute to the formation of 
strong and thick roots. After tillering, however, frosts were 
very injurious. He states that hot days with mean daily tem- 
peratures above 75° and with maximum temperatures above 
86° between the ''earing" and milk stage endangered the 
yield of oats, especially if there were a number of such days 
in succession. A similar temperature after the milk stage 
may cause a falling out of the grains. 

411. In England. — The following is quoted from R. H. 
Hooker and agrees with the results obtained in the United 
States : 



WEATHER AND YIELD OF GRAINS 179 

Oats are similar to barley inasmuch as they urgently require a cool 
summer; the partial coefficients between oats and temperature being 
almost identical with those of barley in the 17th-36th weeks. But 
they differ from barley in requiring rain in the spring; in fact for the 
spring (season) the coefficient with rainfall (+0.70) is just above the 
summer coefficient with temperature (—0.69). Before harvest (25th 
to 32nd week), however, they would seem to like dry weather. There 
are some suggestive negative coefficients with rainfall during autumn. 
Can they mean that seed does not keep well during a damp autumn? 
The coefficients with the preceding summer all seem insignificant. 

Comparing the three cereals, it is noteworthy that with barley and 
oats spring and summer are of preponderating importance, seed-time 
being relatively unimportant: with wheat, on the other hand, there are 
several different periods which may materially affect the crop, the seed- 
time being the most influential. 

RICE 

Rice is a tropical cereal and thrives best in regions of great 
heat, heavy rainfall, and high humidity; but can be success- 
fully grown in the warmer parts of the temperate zone. Fully 
93 per cent of the world's production is raised in southern 
and eastern Asia and the nearby islands. 

412. Rice districts in the United States. — The most im- 
portant rice-growing district in the United States is in south- 
ern Louisiana and southeastern Texas, but other locations 
where the crop is cultivated to a considerable extent are in 
north-central California, eastern Arkansas and in the coast 
counties of South Carolina and Georgia. 

413. Temperature and rice. — The great part of the crop 
is cultivated where the mean summer temperature is over 75° 
to 77°, although certain varieties are grown in Japan where 
the average is not over 70°. The maximum temperature lim- 
its are unknown, but the minimum limits are of great impor- 
tance. At temperatures lower than 46° to 50°, the tender 
leaves are partially arrested in growth and the greener parts 
of the stem turn yellow. The maximum rate of growth cor- 
responds to the highest minimum temperature and where 
there is a lowering of the minimum below the critical point 
there is a decrease in all its functional activities. It requires 
a growing season of at least 135 days. 

414. Water requirement. — The largest rice regions have 
an annual rainfall of 50 inches, and a rainfall of 5 inches a 
month during the growing season. Irrigation is necessary 



180 AGRICULTURAL METEOROLOGY 



f 



in the United States. In the Atlantic Coast districts the fields 
are flooded as soon as the seed is planted to cause sprouting; 
this is called the "sprout" flood.. The water remains from 
6 to 12 inches deep over the fields until the small white 
sprouts show through the hulls. The fields are then drained 
to prevent rotting. A little later the second flooding called 
the ''point" or ''stretch" flood is given. After the plants 
are about 6 inches tall, the water level is lowered to about 4 
inches deep and it is held at this depth from fifteen to thirty 
days. The average length of the irrigation season in the Mis- 
sissippi Valley and Texas is about eighty-six days. 

RYE 

Rye is adapted to a wide range of climate, but by nature 
it is a plant of high latitudes and cool climates. Fully 99 per 
cent of the crop in the United States is fall-sown. 

415. Range in the United States. — The bulk of the pres- 
ent rye production in the United States is from New Jersey 
and New York westward to North Dakota. The northern 
limit follows rather closely the mean winter temperature line 
of 15° in Wisconsin and Michigan, but in northwestern Min- 
nesota it is grown where the mean winter temperature is 
about zero and a temperature of 40° below zero is occasion- 
ally reached. 

416. Weather and rye. — Rye may be sown later in the 
fall than wheat, as it will germinate more quickly and at a 
lower temperature. It will germinate and grow with a tem- 
perature but little above freezing, when wheat would be prac- 
tically at a standstill. Rye in the milk is not damaged by 
light frosts. 

417. Rye in Wisconsin. — A correlation of weather with 
the yield of rye in Wisconsin for the period from 1891 to 1917 
shows the following: 

Table 25. — Correlations between Temperature and Rainfall and 
Yield of Rye in Wisconsin, 1891 to 1917 



Month 

April 
May 
June 


Rainfall 
Correlation 
coefficient 

-0.40 

+0.29 

-0.14 


Probable 
error 
±0.11 
±0.12 


Tem,perafA 
Correlation 
coefficient 

+0.14 

—0.11 

-0.43 


lire 
Probable 
error 


±0.11 



WEATHER AND YIELD OF GRAINS 181 

Tliis indicates that dry weather in April and cool weather 
in June are the important factors in the growth of rye in Wis- 
consin. 

Experiments in Russia showed that for the best develop- 
ment rye needs abundant moisture and heat before the forma- 
tion of the heads; cool and damp weather during the forma- 
tion of the heads; moderate temperature and dry weather 
during blooming as it does not fill well if it rains while in 
bloom, and moist and warm weather during the ripening pe- 
riod. 

GRAIN SORGHUMS 

Grain sorghums are of tropical origin and are at home in 
regions with a rather dry, hot, and sunshiny climate. They 
are able either to resist or escape drought damage by their 
ability to suspend growth during periods of protracted 
drought without being destroyed, recovering and making 
good growth and fair yield when rain comes. Broom-corn is 
most profitable where there is but little rain at the time of har- 
vest as otherwise the heads are apt to be discolored. 

418. Temperature and sorghums. — The grain sorghums 
are sensitive to low temperatures and will not do well at high 
altitudes because of cool nights. The northern or upper limit 
of Kafir is a mean summer temperature of about 75° and that 
of milo is about 70°. 

419. Range in the United States. — The lower Great Plains 
is the home of most of the grain sorghums raised in this coun- 
try. In that region the summer temperatures are high, the 
percentage of possible sunshine great, the annual rainfall from 
15 to 30 inches, and the frequent summer droughts are in- 
tensified by hot winds and excessive evaporation. The bulk 
of the crop is within the rainfall lines of 15 to 30 inches. 

WHEAT 

Wheat is the great bread cereal of the moderate temperate 
climates. In prehistoric times it had spread over Asia and 
Europe. Wheat has been found in tlie vegetable remains of 
the Lake Dwellers, and grains in the tombs and illustrations 
in the bas-reliefs on monuments show that it was raised in 
Egypt three or four thousand years before Christ. 

420. Range. — Wheat is grown in Europe as far north as 
latitude 65°; in North America, to 50° north latitude; and in 



182 



AGRICULTURAL METEOROLOGY 




WEATHER AND YIELD OF GRAINS 183 

South America and Australia nearly to 45° south latitude. 
It is raised within the tropics in Mexico, the Philippines, 
Egypt, India, and central Africa. 

421. In the United States.— Figs. 49 and 50 show the 
distribution of wheat in the United States. These make 
plain that the most important center of winter wheat produc- 
tion is in west-central Kansas, and of spring wheat in nor- 
thern and eastern North Dakota and northeastern South Da- 
kota. 

422. Distribution as affected by temperature. — The di- 
viding line between the principal spring and winter wheat- 
producing areas east of the Rockies agrees closely with the 
mean winter temperature line of 20° or the mean daily mini- 
mum temperature line of 10°. The southern border of the 
winter wheat belt agrees closely with the isotherm of 68° for 
the two months preceding the date of harvesting. The nor- 
thern limit of spring wheat agrees approximately with the 
mean summer temperature of 58°, which is found in the Uni- 
ted States only in the western mountains. Wheat will yield 
a crop, except in unusual years, at elevations up to 8,000 feet 
in the central Rocky Mountain regions where the mean tem- 
perature for the year is not below 38°, and where the mean for 
the summer season is not below 58°. In India the soil tem- 
perature at seeding time is very important in the production 
of winter wheat. When sown too early while the ground is 
warm, plants may start well but will soon decay and be at- 
tacked by white ants. It is considered safe to seed when the 
temperature of the soil has fallen to about 25° C. (77° F.) but 
not when it is as high as about 30° C. (86° F.). 

423. Distribution as affected by moisture. — Most of the 
important wheat districts of the world have an annual pre- 
cipitation of less than 30 inches. In Australia the main wheat- 
producing areas receive less than 20 inches of rain during 
the growing months and in New South Wales and Victoria 
the chief areas are where the winter rainfall is between 10 and 
15 inches. The intensive winter wheat-producing areas in 
Kansas and Nebraska receive an annual rainfall of 20 to 30 
inches, while in the central Mississippi and Ohio valleys the 
amounts are somewhat greater. The most important spring 
wheat areas in South Dakota and Minnesota have an annual 
rainfall of 20 to 30 inches, while in most of North Dakota the 



184 



AGRICULTURAL METEOROLOGY 




WEATHER AND YIELD OF GRAINS 185 

fall is between 15 and 20 inches. In this state, however, 
about one-third of the annual rainfall is received during the 
three spring months and fully one-half of the annual fall 
comes during March to June, inclusive. 

The successful growth of wheat is not limited by heavj^ 
rains, but other crops are usually found to be more profitable 
in regions of heavier rains, and, as in our southern states, 
where the annual rainfall is 45 inches or more, rusts and fun- 
gus diseases are prevalent due to warm and moist springs. 
It has been found in India that good soil aeration, by means 
of which the soil organisms and the roots of the wheat plant 
can obtain abundant oxygen, is quite as important as the 
water supply. It seems that any interference with aeration 
at ripening time prevents maturing and tends to increase rust 
attacks. 

In general, a hot dry climate produces a fine-stemmed 
plant the grain of which is hard, glassy, and rich in nitrogen, 
while a cool moist climate produces a coarser-stemmed plant 
with the grains relatively soft and mealy and poor in nitro- 
gen. 

424. Dates of seeding and harvesting. — The work of 
seeding and harvesting wheat is being carried on in some 
parts of the world during every month of the year, as is shown 
by the following table: 

Table 26. — Where Wheat is Being Harvested 
Month Country 

January Australia, New Zealand, Chili. 

February India, Egypt. 

March India, Egypt. 

April Africa, Asia, Mexico, Cuba. 

May Central Asia, China, Japan, extreme south- 
em United States. 

June Southern Europe, southern and central 

United States. 

July Central Europe, Northern United States, 

Canada. 

August Western Europe, Canada, extreme northern 

United States. 

September Northern Europe. 

October Northern Europe. 

November Western and southern South America. 

December Southern South America. 



186 



AGRICULTURAL METEOROLOGY 



Figs. 51 and 52 show the average dates of beginning of seed- 
ing and harvesting spring wheat in the United States, and 
Figs. 53 and 54 similar data for winter wheat. Winter wheat 
can be seeded too early and also too late for the best results, 
while between there is an optimum or best date for seeding 
in an average year. 

425. The best date to seed winter wheat. — There is usu- 
ally greater danger by winter killing of late-sown wheat than 










Fig. 51. — Average date when the seeding of spring wheat begins. 



of early-sown, especially with a dry fall, as there may be a 
failure to establish a good root system ; the probablity of good 
tillering is also reduced. On the other hand, wheat seeded too 
early is subject to damage by the hessian fly in some districts. 
Fig. 55 shows the date for seeding which will, in the normal 
year, reduce or avoid injury by the hessian fly and probably 
give a greater yield. By comparing the charts, it will be seen 
that the safest date in much of the winter wheat belt is from 
ten to twenty days later than the date when seeding usually 
begins. The state entomologist should be consulted, how- 
ever, as to the prevalence of the hessian fly and its activities. 
426. Important periods of growth. — Well-recognized 
stages in the development of grains are germination, tiller- 



WEATHER AND YIELD OF GRAINS 



187 




188 



AGRICULTURAL METEOROLOGY 



ing, jointing, heading, blossoming, and ripening. Records 
covering thirty years show that in northwestern Ohio the 
length of the period from seeding of winter wheat until the 
plants appear averages nine days; from the appearance above 
ground until blossoming 253 days; from blossoming until ripe 
twenty-six days. 

427. Fruiting period. — In Kansas the fruiting period or 
average length of time between heading and ripening of fif- 







Fig. 53. — Average date when the seeding of winter wheat begins, 

teen varieties of winter wheat is twenty-nine days. The fruit- 
ing period varies for the different varieties from twenty-five 
to thirty-four days. In Ohio the average time between head- 
ing and ripening of one variety is thirty-six days. The 
fruiting period for four varieties of spring wheat in North 
Dakota averages thirty-five days. 

428. Days from sowing to harvesting. — The total num- 
ber of days from sowing to harvesting east of the Rocky 



WEATHER AND YIELD OF GRAINS 



189 




190 



AGRICULTURAL METEOROLOGY 




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WEATHER AND YIELD OF GRAINS 191 

Mountains varies from 250 to 290 days for winter wheat, and 
120 to 130 days for spring wheat. The time for spring wheat 
is from 130 to 180 days in the Pacific states. Some varieties 
of spring wheat will mature grain in 100 days at Fairbanks, 
Alaska, two degrees from the Arctic Circle. 

429. Critical periods of growth. — All authorities agree 
that the wheat plant must have an abundance of moisture at 
the heading stage. Some would place the most critical stage 
just as the plants are beginning to head, others between the 
boot and bloom periods and still others between the bloom 
and milk. It was found in Utah that the period prior to the 
boot stage is very critical. If the plant is injured by drought 
at this time, it does not recover even if given water later; the 
yield of grain is affected more than the yield of straw. High 
temperature and lack of moisture while in bloom produce 
sterile heads. 

430. Moisture and wheat. — It is agreed by different in- 
vestigators that wheat needs only sufficient moisture during 
the first six weeks of its life to keep it growing vigorously. A 
strong root system is obtained by a moderate amount of 
moisture although it needs sufficient during its early stages 
of growth to induce tillering. 

It is advised in Utah to begin irrigation when the plants are 
6 to 8 inches high and to stop at about the time that it comes 
into bloom. It was found in Nevada that the greater yields 
were obtained by a 6-inch irrigation before heading and a 
12-inch after heading. During about forty to sixty days be- 
tween the first six weeks and the last three weeks of its growth, 
the plant should have its greatest moisture. 

Soft wheats are usually less able to endure drought, hot 
winds, and severe winter-killing than hard wheats. Hard 
wheats, for example, are best adapted to central and western 
Kansas, while soft wheat is better in eastern Kansas. Warm 
and wet weather in midsummer is likely to promote an epi- 
demic of rust. Rust is an injurious disease in the southeast- 
ern states and the factor that limits the successful culture in 
warm humid regions. 

431. Weather and spring wheat. — Spring wheat is grown 
in regions where the winters are cold and comparatively dry, 
and where there is little snow for the protection of winter 
grains. Durum wheat is a sub-species that is adapted to re- 



192 



AGRICULTURAL METEOROLOGY 



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gions of low rainfall, rather high summer temperatures, and 
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Fig. 58. — Combined effect of the temperature for June and the rain- 
fall for May and June on the yield of Spring wheat in North 
Dakota. 1891-1913. 



conditions are found in the northwestern Great Plains 
region. 

432. Rainfall and spring wheat (Blair). — ^Figs. 56 and 57 
show the relation between the rainfall during May and June 



WEATHER AND YIELD OF GRAINS 



195 



and the yield of spring wheat in North Dakota and South 
Dakota, respectively, as noted by T. A. Blair in 1913 and com- 



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Fig. 59. — Combined effect of the temperature for June and the rain- 
fall for May and June on the yield of spring wheat in South Dakota, 
1891-1913. 

pleted in 1918 by the author. These indicate that relatively 
dry weather in these states during May and June is almost 
invariably followed by a low yield of wheat, while an abundant 
rainfall is usually followed by a good yield. In Minnesota, on 



196 



AGRICULTURAL METEOROLOGY 



the other hand, there is Httle relation between the rainfall for 
May and June and the yield of wheat. 

433. Temperature and spring wheat (Blair). — Figs. 58 
and 59 indicate the effect of the rainfall for May and June and 
the temperature in June in varying the yield of spring wheat 
in North Dakota and South Dakota, respectively, for the pe- 
riod from 1891 to 1913, inclusive. 

434. In North Dakota. — Fig. 58 shows that there were 
seven years during this period with the average temperature 
in June higher than the normal and that in every case the 
wheat yield was below the normal. There were fifteen years 
with the temperature lower than normal and in eleven of 
these the yields of wheat were above the normal. 

435. In South Dakota. — Fig. 59 shows that there have 
been some good yields of wheat in South Dakota when June 
was warmer than normal, but when June was cool there was 
a greater percentage of good yields in this state than in North 
Dakota. In North Dakota there were ten years with June 
cool, and May and June wet, and in eight of these years the 
yield of wheat was greater than normal. In the six years in 
South Dakota when June was cool and May and June wet, 
every year gave a wheat yield above the normal. 

The following table gives the results of a correlation of 
weather with the yield of spring wheat: 



Table 27. — Correlation Coefficients Between Spring Wheat 
AND Rainfall and Temperature (T. A. Blair) 



North Dakota 

May and June 

May 

June 

July 



Rainfall 
Correlation Probable 
coefficient error 

{1892-1912) 
0.63 ±0.09 

0.48 ±0.11 

0.35 ±0.13 

0.30 ±0.13 



Temperature 
Correlation Probable 
coefficient error 

(1892-1913) ' 

-0.39 ±0.12 

0.02 ±0.14 

— 0.67 ±0.08 

-0.19 ±0.14 



South Dakota 
May and June 
June 



(1891- 
0.59 
0.35 



-1912) 

±0.09 
±0.13 



(1891-1913) 
— 0.62 ±0.09 

-0.73 ±0.07 



WEATHER AND YIELD OF GRAINS 197 

Table 27. — Correlation Coefficients Between Spring Wheat 
AND Rainfall and Temperature (T. A. Blair) — Continued 

Rainfall Temperature 

Correlation Probable Correlation Probable 
coefficient error coefficient error 

Minnesota (1891-1912) 

May andJune —0.02 ±0.14 

May and June 
(omitting 4 wet- 
test years) 0.26 ±0.13 

North Dakota {1892-1917) 

May and June 0.61 ±0.08 

June —0.45 ±0.11 

South Dakota (1891-1917) 

May and June . 49 ±0.10 

June —0.62 ±0.08 

This table clearly shows the importance of cool weather in 
June and an abundance of moisture in May and June in the 
Dakotas. 

436. Weather and spring wheat, 1918.— The effect of the 
weather in 1918 on the condition of spring wheat in the states 
of North Dakota and South Dakota is indicated in Fig. 60. 
The variation of the average monthly temperature and the 
total monthly rainfall from the normal is shown for the months 
of March to July in each state. The dots showing the condi- 
tion of spring wheat on June 1, as compared with the ten- 
year average are placed on the vertical line indicating the de- 
partures of the temperature and rainfall from the normal for 
the month of May, because the condition on June 1 is the 
result largely of the weather during May. For the same rea- 
son the dots for July 1 and August 1 are placed on the June 
and July lines, respectively. 

437. Dry weather detrimental. — While there was a steady 
advance in the condition of wheat in South Dakota due to 
the generous rainfall throughout the season, it is evident that 
the deficient rainfall in June in North Dakota was responsi- 
ble for the lack of improvement in wheat in this state. Fre- 
quently the condition of this crop will be lowered to a marked 



198 



AGRICULTURAL METEOROLOGY 





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SOUTH DAKOTA 


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Fig. 60.— Effect of the weather on the condition of spring wheat in 
North Dakota and South Dakota in 1918. See the note under 
Fig. 34 for an explanation of the various hues, except that in Fig. 60 
monthly instead of weekly rainfall and temperature conditions are 
indicated. 



WEATHER AND YIELD OF GRAINS 199 

extent by insufficient moisture in two successive months, as 
was the case in Montana in 1917. 

438. Weather and spring wheat in Manitoba, Canada. — 
From studies in the field in Manitoba, Connor found that ''if 
in the earher stages of growth it is cool and rainy, the head- 
ing will be delayed, and the yield will be heavy, but if warm 
and dry, heading is hastened and the yield will be light." He 
correlated the rainfall, range of temperature, and minimum 
temperature for successive thirty, sixty, ninety, and 120 day 
periods with the yield of spring wheat in Manitoba. The 
record covered the time from 1883 to 1917 and the highest 
correlation for the thirty-day period was for the third thirty 
days after seeding. The values were: 

Correlation Probable 
coefficient error 

Rainfall 0.42 ±0.11 

Range of temperature — . 55 =t=o . 10 

Minimum temperature — . 40 =*=0 . 12 

He fixes the average time of the critical period as the last 
week in June and the first three weeks in July, and the crit- 
ical factor in wheat production in Manitoba the ''variability 
of early July weather." 



Winter wheat 

439. The effect of weather on the yield of winter wheat. — 

The opinion is frequently expressed that the yield of winter 
wheat will be greatly affected by a warm or cold fall or win- 
ter, or by the temperature or rainfall of a single month or 
group of months. 

440. Comparison of records in Ohio for fifty-four years. — 
In order to determine the ground for these opinions, correla- 
tions were made by the author between the weather factors 
for different periods and the yield of wheat in Ohio for the 
years from 1860 to 1913, inclusive. 

Table 28 shows the correlation coefficients between the 
average rainfall and temperature and the wheat yield for the 
state of Ohio. 



200 



AGRICULURAL METEOROLOGY 



Table 28- 


-Correlation 


OF Weather and Winter Wheat for the 




State 


OF Ohio, 1860 


TO 1913 




Precipitation 


Temperature 


Period 


Correlation 


Probable 


Correlation Probable 




coefficient 


error 


coefficient error 


September 


0.04 


±0.09 


0.16 ±0.09 


October 


0.16 


±0.09 


0.09 ±0.09 


November 


-0.02 


±0.09 


0.14 ±0.09 


December 


-0.17 


±0.09 


0.05 ±0.09 


January 


0.09 


±0.09 


0.21 ±0.09 


February 


0.01 


±0.09 


0.26 ±0.08 


March 


0.06 


±0.09 


0.46 ±0.07 


April 


0.02 


±0.09 


— 0.10 ±0.09 


May 


0.02 


±0.09 


-0.11 ±0.09 


Autumn 








(Sept. to 








Nov.) 


0.17 


±0.09 


-0.03 ±0.09 


Winter 








(Dec. to 








Feb.) 


-0.17 


±0.09 


0.17 ±0.09 


Spring 


^ 






(March 








to May) 


0.15 


±0.09 


0.19 ±0.09 



441. Precipitation and yield. — It will be seen that the 
correlation coefficient for rainfall is not high enough for any 
month or group of months to show any relation to the yield. 
In other words, the precipitation in Ohio is not the determin- 
ing factor in wheat yield. The precipitation is always suf- 
ficient and never so great as to affect the yield materially. 

442. Temperature and yield. — The table also shows that 
the average temperature for a month, or for the group of 
months designated as "season," is not the all important 
factor in affecting the yield. 

443. Mean temperature for March. — The most impor- 
tant weather factor in the table is the mean temperature for 
March. This gives a correlation coefficient slightly more than 
seven times the probable error and so can be said to have a 
marked influence on the yield. Fig. 61 gives the dot chart 
showing the relation between these factors. An inspection 



WEATHER AND YIELD OF GRAINS 



201 



of this chart makes plain that a warm March has been fol- 
lowed by a wheat yield above the normal twenty-one times 
out of twenty-four, or 88 per cent of the time. On the other 
hand, when March averages colder than the normal, the yield 



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YJELO OF WH£AT 



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20 



22 



Fig. 61. — Relation between the mean temperature for March and 
the yield of winter wheat, Ohio, 1860 to 1915. 



of wheat will be below the normal 63 per cent of the time. 
When March averaged 2 degrees a day or more above the nor- 
mal, the probability of the yield of wheat being above the 
normal in Ohio is 94 per cent, covering a period of fifty-six 
years. When March averages 2 degrees or more a day cooler 



202 AGRICULTURAL METEOROLOGY 

than the normal, the probability of the wheat yield being 
above the normal is only 25 per cent. 

444. March temperature in other states. — A similar 
study, though covering a shorter period of time, shows no 
such relation between the March temperature and wheat 
yield in Maryland and Delaware, Illinois, Nebraska, Iowa, 
Kentucky, or Oklahoma. 

445. Effect of a snow cover. — A thorough study of the 
effect of a covering of snow during the winter as a whole and 
for different months, shows that a lack of snow on the ground 
with freezing and thawing weather is not such a detriment as 
has been believed. Instead, a lack of snow covering in Jan- 
uary seems to be beneficial, possibly because the earth thus 
settles around the roots and makes the plant better able to 
stand later unfavorable weather. The correlation coefficient 
for Wayne County, Ohio, between the number of days with- 
out snow cover and with the minimum temperature below 
freezing with the yield of wheat is -1-0.49, probable error 
=1=0.11. This is not conclusive, however, and should be given 
further study. 

446. Snowfall as affecting wheat yield. — Snowfall is con- 
sidered favorable for winter wheat especially if it comes late 
in the spring. The following table seems to controvert this 
idea: 

Table 29. — Correlation Between Snowfall and the Yield of 
Wheat. 1892-1914 



Period and place 


Correlation coefficient 


Probable error 


Jan., Fulton Co., Ohio 


0.42 


±0.13 


Feb., 


0.12 


±0.15 


March, " 


-0.84 


±0.04 


" Wayne Co., " 


— 0.69 


±0.08 


" Seneca Co., " 


-0.48 


±0.11 



This indicates that a heavy snowfall in January is favor- 
able even though a large number of days with a snow cover- 
ing has an opposite effect. 

447. Snowfall in March detrimental. — The most remark- 
able fact in this table is the evidence that snow falling in 
March is decidedly unfavorable to winter wheat as shown by 
the high negative value for the correlation coefficient. This 



WEATHER AND YIELD OF GRAINS 



203 



is brought out more clearly in Fig. 62 which shows the rela- 
tion between the snowfall for March and the yield of wheat 
in Fulton County, 1892 to 1914. In nearly every case when 
the snowfall is above the normal, the yield of wheat is corre- 
spondingly below. The figures at the left show both inches of 
snow and bushels of wheat. A similar correlation between 
the March snowfall and the wheat yield in other northern 

















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Fig. 62. — Relation between the snowfall in March and the yield of 
winter wheat in Fulton County, Ohio, 1892-1914 

Ohio counties gives much the same result, although no such 
marked effect has been found in other states. 

448. In Indiana. — Cool weather during the month of 
April is decidedly favorable for winter wheat in Indiana. In 
the thirty-two years from 1887 to 1918, April was cooler than 
the normal eighteen times. Following the cool Aprils, the 
wheat yield was above the normal thirteen times and below 
five times. Following the fourteen warm Aprils, the yield 
was above the normal seven times and below seven times. 

449. Cool and wet favorable in Indiana. — Of cool Aprils, 
the most beneficial appears to be those with an excess of pre- 
cipitation, as following nine cool and wet Aprils the yield of 



204 



AGRICULTURAL METEOROLOGY 



wheat was above the normal seven times and below twice. 
For the state, 2° in temperature and 1.25 inch of precip- 
itation, mark the average departures from the normal. Con- 
sidering departures greater than this as abnormal, it is found 
that only one wheat crop out of seven has been below the 
average after an abnormally cool April, also only one crop 
out of five has been below the normal following an abnor- 
mally wet April. 

450. A cool May also beneficial in Indiana. — Of fifteen 
cool Mays, the wheat crop was above the average twelve 
times, eight of the twelve following cool wet Mays. 

451. In Missouri. — The following tabulations show the 
relation between weather and the yield of wheat in Missouri 
for the months indicated, covering a period of thirty-one years : 

Table 30. — Correlation between Weather and Yield of Wheat in 

Missouri 



No. 



of yean 


March 
J Weather 


Yield above 
normal 


Below normal 


8 
7 
8 
8 




warm and dry 
cold and dry 
warm and wet 
cold and wet 


6 
1 
3 
4 


2 
6 
5 
4 


10 
10 

4 

7 


April 


warm and dry 
cold and dry 
warm and wet 
cold and wet 


5 

4 

1 
4 


5 
6 
3 
3 


7 
6 
9 
9 


May 


warm and dry 
cold and dry 
warm and wet 
cold and wet 


4 
4 
2 
4 


3 
2 

7 
5 


11 
6 
5 
9 


June 


warm and dry 
cold and dry 
warm and wet 
cold and wet 


6 
3 
1 
3 


5 
3 
4 
6 



452. May warm and dry most favorable in Missouri. — 

If only these years are considered when the mean tempera- 
ture for May has varied 1.5° or more from the normal and 



WEATHER AND YIELD OF GRAINS 205 

the precipitation 1.50 inches or more from the normal, the 
following results: 

Table 31. — Correlation between Weather in May and Yield of 
Winter Wheat 





May 


Years with yield 


Years 


Weather 


Above normal 


Below normal 


4 


warm and dry 


4 





1 


cold and dry 





1 


3 


warm and wet 





3 


3 


cold and wet 


1 


2 



The average yield of wheat in Missouri is 13 bushels to the 
acre. If only those years are considered when the yields va- 
ried 2.5 bushels or more from the normal, the following results 
are obtained: 

Table 32. — Correlation between Weather and Yield of Winter 
Wheat when Latter Varied 2.5 Bushels or more from Normal 
May Yield 

Years Weather A hove normal Below normal 

3 warm and dry 3 

3 cold and dry 2 1 

6 warm and wet 1 5 

1 cold and wet 1 

These data seem to indicate that relatively warm and dry 
weather in May is needed in Missouri for the best yields of 
winter wheat. 

453. In Kansas. — Investigations at the Fort Hays Ex- 
periment Station, Kansas, indicated that in western Kansas 
moisture is the limiting factor in the production of winter 
wheat. In a four-year stud}^, it was found that the yield of 
grain was in direct proportion to the supply of available mois- 
ture at seeding time. 

454. Summer rain and yield of wheat in Kansas. — At 
the Fort Hays Station, which is not far from the center of the 
wheat area of the Plains districts, 75 per cent of the total an- 
nual rainfall is received between April 1 and September 30. 
At Wallace, Kansas, about 65 per cent of the annual fall 
comes in May, June, July, and August, while in Lincoln, Ne- 
braska, nearly 60 per cent falls in these four months. It was 
learned at Fort Hays that if the methods of handling the soil 
are such as to allow for the maximum absorption of the sum- 



206 



AGRICULTURAL METEOROLOGY 



mer rainfall, and to reduce the evaporation to a minimum, 
the yield of winter wheat will be affected to a marked degree. 
455. Rainfall and temperature by months. — H. B. tan- 
ning made a careful study (unpublished) of the effect of the 
weather on the yield of wheat over an area including thirty- 
seven counties in the important wheat district of central Kan- 
sas. Dot charts were prepared for both temperature and 



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YIELD- BUSHELS PER ACRE | 

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Fig. 63. — Relation between the rainfall for July of one year and for 
April of the following spring and the yield of wheat for that season, 
Kansas 1893-1917. 

rainfall for each month and for groups of months from July 
preceding planting of wheat until the following June. 

456. No temperature relation. — These charts showed no 
apparent relation between the mean temperature for any 
month and the wheat yield. In other words, the average tem- 
perature for any month does not vary enough from the nor- 
mal to have its favorable or unfavorable effects shown in the 
harvest often enough to be of importance. 

457. Rainfall and yield in Kansas. — No appreciable re- 
lation was found between the yield and the rainfall for any 
of the nomths except for July preceding planting and for 
April preceding harvesting, and in these months the relation 
is slight. The yield increases in a general way as the rainfall 
for the preceding July increases, until the rainfall reaches 



WEATHER AND YIELD OF GRAINS 



207 



about 6 inches and the yield 13 bushels to the acre, but higher 
yields are always with less rainfall. The lowest and the high- 
est yields of wheat in central Kansas have occurred when the 
rainfall of the preceding July for that district was about one 
inch. Charts showing the yield and the rainfall for July and 
August, and July, August, and September also indicate a 
fairly regular increase in yield with increasing rainfall until 
about 13 or 14 bushels to the acre, and then higher yields 
have always been with less rainfall. 

458. July and April combined. — Fig. 63 shows the rela- 
tion between the rainfall for July preceding and April of the 
year of harvest, and the yield of wheat in Kansas from 1893 
to 1916-17. With three or four marked exceptions, there is a 
fairly close relation. 

The following statements of weather conditions favorable 
or unfavorable for winter wheat in Kansas, by months, are 
from S. D. Flora, meteorologist of the Weather Bureau: 

Table 33. — Conditions Favorable and Unfavorable to Winter 
Wheat in Kansas 



Month 


Condition favorable 


Condition unfavorable 


January 


Snow cover, abundance 


High winds, if dry. 




of moisture. 


Freezing and thawing 
without snow cover. 


February 


Same as January. 




March 


Cool and wet as it pro- 


Abnormally warm, es- 




motes stooling 


pecially with high winds; 
heaving. 


April 


Plenty of moisture and 
temperature near normal. 




May 


Warm and sunshiny 


Cold and wet favors 
black stem rust. 


June 


Warm and dry 


Excessively high tem- 
perature which shrivels 
the grain. 


July 


Warm. 


Wet delays harvest. 


August 


Dry for threshing, abun- 
dant moisture for preparing 
ground for next crop. 




September 




Prolonged dry spell. 


October 


Abundant moisture. 




November 


Abundant moisture; 


A cold period without 


December 


snow cover. 


snow. 



208 AGRICULTURAL METEOROLOGY 

459. In Iowa. — February is a very critical month for 
winter wheat in Iowa. A correlation between the weather 
and the surviving winter wheat acreage for twenty years 
gives the following result: 

Table 34. — Correlation between Weather aistd the Surviving 
Winter Wheat in Iowa 

February 

Weather Correlation coefficient Probable error 

Mean temperature 0.41 ±0 . 12 

Average rainfall 0.46 ±0.12 

Snowfall 0.36 ±0.12 

The mean temperature was above the normal in February 
in the southern third of Iowa eight times and the surviving 
wheat acreage was above the normal every time. A warm 
and wet February is decidedly favorable for winter wheat in 
Iowa. 

460. In Wisconsin. — A correlation between weather and 
winter wheat in Wisconsin for the period from 1891 to 1917 
shows the following: 

Table 35. — Correlation between Weather and Winter Wheat in 

Wisconsin 
Month Precipitation 

Correlation Probable 

coefficient error 

April -0.14 

Mav 0.14 ■ 

June -0.03 • 



Temperati 


ire 


Correlation 


Probable 


coefficient 


error 


0.07 





-0.12 
—0.42 




±0.11 



This indicates that a cool June is decidedly favorable for a 
good wheat yield in this state. 

461. Winter-killing of grains. — Winter damage to fall- 
sown grains is usually grouped under four main heads: (1) 
heaving, (2) smothering, (3) direct effect of low tempera- 
tures on the plant tissue and protoplasm, and (4) physiologi- 
cal drought. 

462. Heaving is one of the most common causes of dam- 
age especially on poorly drained, heavy soils. It occurs usu- 
ally in the spring, and is due to alternate freezing and thaw- 



WEATHER AND YIELD OF GRAINS 209 

ing. The plants are lifted from the soil when it expands, and 
as a result the roots are broken and exposed to the air. Heav- 
ing is a common cause of winter-killing in the eastern part of 
the United States. 

463. Smothering is believed to be a frequent cause of in- 
jury when the ground is covered with an ice sheet; instances 
have been reported where smothering has resulted from a 
very deep snow-cover. The damaging ice-sheet more fre- 
quently results from melted snow, although injury is some- 
times caused by a storm of sleet and rain, which freezes nearly 
as rapidly as it falls. 

464. Freezing of plants. — There can be no doubt that 
plants are often killed by the direct effect of cold on the tissue, 
without heaving, smothering, or physiological drought tak- 
ing place. The injury usually increases with the degree of 
cold and its duration. The effect of a sudden freeze follow- 
ing a warm period is sometimes damaging, especially in the 
latter part of the winter or early in the spring, when a sharp 
drop in temperature follows a period of unusual mildness. 

465. Physiological drought causes injury during dry 
spells in winter. Differences in resistance of certain cereals 
may perhaps be explained by their ability to absorb a larger 
amount of water from the soil in proportion to that transpired. 

466. Winter wheat in 1919. — Fig. 64 shows the varying 
temperature and rainfall in Kansas and Indiana from August, 
1918, to May, 1919, and the condition of winter wheat on the 
1st of December, April, May, and June. Exceptionally fa- 
vorable weather for the growth of wheat prevailed in all sec- 
tions of the central wheat-growing area throughout the entire 
season. The soil was in excellent condition during the late 
summer and fall of 1918 for the preparation of seed-beds, 
germination of seed, and early growth of the young plants, 
and consequently the crop entered the winter in excellent 
condition with the roots well established. The winter was 
mild, with sufficient soil-moisture available, and the spring 
months were uniformly favorable for growth. The condition 
of the crop was exceptionally high on the first of April, 1919. 

467. Yield disappointing. — The yield of winter wheat, 
however, did not come up to expectations, especially in the 
central and eastern portions of the belt, as compared with the 
indications a short time before harvest. It was quite disap- 



210 



AGRICULTURAL METEOROLOGY 



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WEATHER AND YIELD OF GRAINS 211 

pointing as to both quantity and quality. Under the influ- 
ence of persistent favorable growing weather, there was too 
rank straw growth at the expense of grain in many localities. 
There was considerable lodging and this combined with warm 
dry weather when the grain was in the milk stage and while 
ripening, resulted in many poorly filled heads and much 
shriveled grain. As harvest approached there was an increase 
in disease, particularly scab and rust. 

468. Weather and hessian fly damage. — A correlation 
between the weather in September and October and the dam- 
age done by the hessian fly the following year in two counties 
in Ohio, during the period from 1895 to 1913, is shown below: 

Table 36. — Correlation between Weather and Hessian Fly 

Damage 



Rainfall 




Temperature 


Correlation Probable 


Correlation Probable 


coefficient 


error 


coefficient error 


Adams Co. 






September 0.02 


=t0.15 


0.24 ±0.14 


October —0.13 


±0.15 


0.53 ±0.11 


Fulton Co. 






September —0.23 


±0.14 


0.09 ±0.14 


October 0.36 


±0.13 


0.34 ±0.14 



The only correlation that is high enough to be considered 
is with temperature in October in Adams County. This 
shows that a warm October is favorable for the development 
of the fly. 

469. Rainfall and yield of wheat in Australia. — The aver- 
age yield of wheat in the state of Victoria for the twenty-five 
years from 1890 to 1914 was 9.1 bushels to the acre, while the 
average rainfall for the winter months. May to October, for 
1890 to 1915 was 9.5 inches. 

A. E. V. Richardson has prepared the following graph, Fig. 
65, to show the relation between the rainfall and the yield 
of winter wheat in that state. He states that this graph 
shows that there has been an improvement in cultural methods 
since the serious drought of 1902; that the best yields have 
been with a rainfall for the six months of between 10 and 13 
inches; that with each inch of rainfall during the first twelve 



212 



AGRICULTURAL METEOROLOGY 



years, a yield of 0.77 bushels was harvested, while during the 
second twelve years the yield for each inch of rainfall was 1.12 
bushels to the acre; and that it seems possible to calculate the 
probable yield of wheat by the' first of November. 

He shows the improvement in farming methods by the fact 
that during the first twelve years the line of yield was always 



GWHELS.r WHEAT 









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wheat in Australia, 1890 to 1915. 



below the rainfall line and during the second period it was 
above with few exceptions. In the fall of 1914, he calculated 
a yield of 13.91 bushels to the acre while the actual yield was 
about 16 bushels to the acre. 

470. In Italy. — Girolamo Azzi has found in the province 
of Bologna, Italy, that there are two critical periods in wheat 
growth: (1) during the two decades preceding heading when 
wheat must have moisture; and (2), the two decades which 
follow the flowering stage (the period of the formation of the 
kernel), when violent rains and high winds will cause lodging 
and a resulting reduction in yield. 

471. In England. — Studies by Gilbert and Lawes, Shaw 
and Hooker, show that a dry autumn (for the climate), a 
warm, dry winter, and a cool spring produce the best condi- 
tions for a good yield of winter wheat. Hooker states that 
''absence of rain during the flowering period and warmth at 
harvest time are wanted for good germinating seed." 



WEATHER AND YIELD OF GRAINS 213 

472. Other factors should be studied. — It must be recog- 
nized that the effect of winter will depend on the condition 
of wheat when winter sets in; that particularly favorable or 
unfavorable weather in the spring and early summer may off- 
set favorable or unfavorable winter conditions, and that there 
may be a short critical period during the formation of the 
heads. 

LABORATORY EXERCISES 

(1) The optimum and extreme temperature for the germination of the 
different grains should be determined. Available experiment station 
data should be supplemented by experiments. 

(2) Crop yield and climatological data should be tabulated and corre- 
lations made, especially for short periods. 

(3) Whenever practicable the character of the weather at about the 
heading time of grain should be recorded and its effect on the growing 
crop noted. It is beheved that the most critical time for small grains 
is at about the blooming time but whether just before or just after has 
not been determined. 

(4) A study is needed of the effect of the weather on grain sorghums 
in the lower Great Plains Region. 



REFERENCES 

Buckwheat. Clyde E. Leighty. Farmers' Bulletin 1062. 1919. 
Corn Crops in the United States. H. Arctowski. Reprint from Bulle- 
tin of the American Geographical Society, October, 1912. 
Effect of Weather upon the Yield of Corn. J. Warren Smith. 

Monthly Weather Review, February, 1914. 
Experiments with Durum Wheat. C. R. Ball. U. S. Department of 

Agriculture Bulletin No. 618, 1918. 
Geography of the World's Agriculture. Finch and Baker. Ofl5ce of 

Fann Management, 1917. 
Montana Experiment Station Bulletin, No, 107. 
National Weather and Crop Bulletins, Weather Bureau. 
Nebraska Experiment Station Research Bulletin No. 6. 
New York Experiment Station Annual Report, 1884-5. 
Partial Correlation applied to Dakota Data on Weather and Wheat 

Yield. T. A. Blair. Monthly Weather Review, February, 1918. 
Rainfall and Spring Wheat. T. A. Blair. Monthly Weather Review, 

October, 1913. 
Autumn rainfall and Wheat, W. N. Shaw. Symons Meteorological 

Magazine, 1905. 
Relation of the Weather to the Yield of Wheat in Manitoba. A. J. 

Connor. Monthly Bulletin of Agricultural Statistics, April, 1918. 



214 AGRICULTURAL METEOROLOGY 

Relation of Moisture to the Yield of Winter Wheat in Western Kan- 
sas, The. Kansas Agricultural Experiment Station Bulletin 
No. 206, 1915. 

Relationship between the .Average Wheat Yield and the Winter Rain- 
fall. A. E. V. Richardson. Journal of Agriculture of Victoria, 
January, 1916. 

Small Grains, The. M. A. Carleton, 1916. 

Temperature and Spring Wheat. T. A. Blair. Monthly Weather 
Review, January, 1915. 

Tennessee Agricultural Experiment Station Twenty-second Annual 
Report. Knoxville, Tenn. 

Yearbooks of the United States Department of Agriculture, for the 
years 1915 and 1917. 

A Statistical Study of Weather Factors Affecting the Yield of Winter 
Wheat in Ohio. T. A. Blair. Monthly Weather Review, December, 
1919. 

Efifect of Snow on Winter Wheat in Ohio. J. Warren Smith. Monthly 
Weather Review, October, 1919. 



CHAPTER IX 

THE EFFECT OF WEATHER ON VEGETABLES AND 
MISCELLANEOUS CROPS 

Vegetables are usually classified as ''hardy" and "tender" 
but a better grouping would be as ''cool" and "warm" 
weather crops. These groups might be further classified in 
regard to their varying need of moisture, sunshine, and tem- 
perature. 

473. Warm-weather crops. — From a temperature point 
of view, warm-weather crops may be divided into two well- 
defined groups: (1) Those with a period of growth so short 
that they may be planted and harvested in the normal warm 
seasons; and (2) those with so long a period of growth that 
they must be started under glass in advance of the normal 
season to mature before fall frosts. 

The following may be classified as warm-season crops as 
they make their best growth during warm weather and should 
not be planted or set out until the ground is warm and all 
danger of frost is over. 

Cantaloupes also need frequent rains. 

Cassava is very sensitive to frost and requires a growing 
season of about seven months. Its cultivation is not practic- 
able outside the southern part of the Gulf states. 

Castor beans are well suited to the climatic conditions of the 
arid southern valleys of Arizona where plants attain the size 
of small trees and live for many years. During frosty weather 
they are dormant or may be killed back somewhat, but re- 
sume growth with warm weather. 

Cucumbers should not be planted until about a month after 
hard frost, when they will grow and produce throughout the 
summer. They need plenty of moisture. 

Eggplants have a long growing season and must be started 
in hotbeds. After the plants are well established, they will 
stand dry and hot weather. 

215 



216 AGRICULTURAL METEOROLOGY 

Gherkins are quite drought-resistant. 

Muskmelons need plenty of moisture. 

Okra may be planted about two weeks after average date 
of last killing frost. They are quite drought-resistant. 

Peanuts are raised where the growing season is long and 
warm. They succeed best south of latitude 36 degrees; and 
are easily killed by frost. 

Pepper plants must be started in hotbeds as they have a 
long growing season. They should not be transplanted until 
the ground is throughly warm. 

Pumpkins will grow and mature during the warm season. 

Squashes are less sensitive to cold than melons and some 
vatieties will not stand excessive heat. 

Sweet potatoes have a long growing season and should not 
be transplanted from the hotbed for about a month after the 
last spring frost. The sweet potato is a subtropical vegetable 
and needs ample sunshine and high temperature for best 
growth. It is unable to stand cold weather and even at a 
temperature of 40° the growth is much retarded. Produc- 
tion in the United States is confined mostly to the southern 
and southeastern states where the growing season is from 150 
to 175 days and the mean summer temperature over 72°. 
The plants make the best growth with frequent moderate 
rains during the late spring and early summer, but should 
have comparatively dry weather while maturing, otherwise 
it inclines the plants to excessive vine growth. 

Tomato plants thrive best at a temperature of 75° to 85° 
during the day and about 60° at night. The fruit does not 
ripen well when the temperature is above 85°. Some studies 
in southwestern Ohio indicate that to produce the best 
yields in that region the month of May should be rather dry 
and cool; June, cloudy and wet; July, cool and wet, and Sep- 
tember, clear and dry and not too warm. Tomato plants 
may safely be transplanted from the hotbed about two weeks 
earlier than eggplants or sweet potatoes. Bright sunshine, 
while tomatoes are in bloom, is favorable for a good setting 
of fruit, while cloudy and rainy weather is unfavorable. 

Watermelons need plenty of moisture and will stand quite 
warm weather. 

474. Cool-weather crops. — Some of these are the winter 
truck crops of the southern and Pacific Coast states and will 



WEATHER AND MISCELLANEOUS CROPS 217 

endure temperatures below freezing without damage. Some 
varieties, however, are injured by frost and should not be 
planted until frost danger is over. 

The cool-weather vegetables are divided into three general 
groups: (1) Short-season crops that cannot endure hot 
weather but will mature during the spring, and in some cases 
in the fall ; (2) this group has a long growing season and must 
either be started under glass and transplanted as early as the 
ground can be worked; planted in the summer and allowed 
to make most of the growth in the fall; be grown as winter 
crops in the South, or as summer crops in the North where 
the season is cool ; (3) relatively long season crops demanding 
cool moist weather chiring their early growth, but capable of 
enduring considerable heat after being well established. All 
of these crops need plenty of moisture. 

Beans. — Although most varieties are very susceptible to 
frost damage and some thrive best in the continuously hot 
interior of California or in the dry districts of Arizona, most 
field and garden beans are best adapted to moderately cool 
moist climates. Yields are seriously decreased by especially 
hot dry periods when the plants are in bloom or when the 
seed-pods are setting. The lima bean grows to perfection in 
California only in the warm humid climate of the southern 
coast regions. The annual rainfall in this area is only 10 to 
15 inches, but the ocean fogs are an important factor. In the 
interior valleys where it is hot and dry, the plants have given 
only a scant setting of pods. The small white or Navy bean, 
on the other hand, succeeds best in the cool humid climate of 
the coast region from San Francisco to Santa Barbara. There 
should be four full months of frost-free weather where beans 
are to be grown. 

Beets. — Garden beets may be planted at about the average 
date of the last killing frost. This belongs to the third group 
mentioned above. 

Cabbage is a winter crop in the South; an earl}^ spring or a 
fall crop in central districts, or a summer one in cool climates. 

Carrots are an early crop that grows in warm weather also, 
but make the best growth late in the season in central dis- 
tricts. 

Cauliflower cannot stand excessive heat. Early cauli- 
flower should be set out a1)out the date of the last average 



218 AGRICULTURAL METEOROLOGY 

killing frost, and late varieties planted in summer for fall 
growth. 

Celery is a winter crop in the South and a full season crop 
in the North where the summers are cool with a large amount 
of moisture. 

Chard is capable of enduring considerable heat after the 
plants have become established. 

Collards may be planted as early as the ground can be 
worked. 

Kale is capable of withstanding considerable heat, but 
should be planted early. 

Kohlrabi is an early planted short-season crop, and cannot 
endure great heat. 

Lettuce heads best in cool weather. Head lettuce can be 
grown in greenhouses far better in eastern Massachusetts 
than in northern Ohio, possibly because of the greater amount 
of cloudy weather in northern Ohio in winter. 

Mustard may be planted two weeks before the average last 
frost date. It is a short-season crop and cannot endure too hot 
weather. 

Onion is one of the hardiest vegetables known. Well-es- 
tablished plants will endure temperatures of 12° to 14° and 
if given plenty of moisture will endure heat well. Onions re- 
quire cool and moist weather in early growth but ripen better 
if it is drier. 

Parsley should be planted about the average last killing 
frost date. It will endure heat if well established. 

Parsnips need a long growing season and ripen properly 
only in cold weather. 

Peas. — While heavy frost will kill the blossoms of most va- 
rieties, these plants will stand a temperature of 22° to 25° if 
not growing rapidly. The smooth peas are more hardy than 
the wrinkled variety. Hooker has found that in England the 
seed is greatly affected by the weather of the summer; it 
should be dry and cool. 

Radishes are a short-season crop and may be grown in the 
spring, or in the fall if given plenty of moisture. They are of 
poor quality in hot weather and are of best quality when the 
soil is 90 per cent saturated; they make stunted poor plants 
when the saturation is 40 per cent, and a complete failure 
when only 10 per cent. 



WEATHER AND MISCELLANEOUS CROPS 219 

Rhuharl) io a perennial crop that needs cool moist weather 
to make the most rapid tender growth. 

Salsify and spinach are relatively long-season crops that 
should be planted about the average date of the last killing 
frost. They will endure considerable heat and drought after 
becoming established. 

Turnips are a short-season crop. They will mature before 
hot weather if planted very early, or may be planted in sum- 
mer and raised as a fall crop. Well-estabUshed plants are not 
severely injured by cold. Some varieties develop the best 
flavor only in the northern states where the nights are cool. 
They need cool and moist weather at seeding time. 

475. Miscellaneous field and garden crops include those 
vegetables wliich cannot be regularly classed as warm- or 
cool-season crops. 

Asparagus is cultivated under a wide range of temperature. 
It is resistant to extreme heat, endures drought, but will not 
endure extremely wet soil. It is one of the oldest vegetables 
known. 

Hops require abundant moisture while making growth but 
sunny and moderately warm weather while the hops are de- 
veloping and ripening. 

Soybeans require about the same climate as corn. The 
pods may not fill well in hot weather in the extreme South. 

Velvet beans grow well only when the weather is warm, and 
the young plants are very susceptible to frost. The higher 
the temperature when the seed is planted, the more rapid will 
be the growth and the shorter the time required to reach ma- 
turity. 

476. Planting dates. — Fig. 66 shows the approximate 
dates for planting vegetables and may be followed with a rea- 
sonable degree of safety. The lines and zone areas are based 
on the last killing frost in the spring for the earliest planting, 
and on the average date of the first killing frost in the fall for 
the latest date. 



220 



AGRICULTURAL METEOROLOGY 




Fig. 66. — ^Planting zones for vegetables in the eastern half of the 
United States. While these are the best dates, earlier and later 
plantings can be made with fair chance of success. 



WEATIWR AND MISCELLANEOUS CROPS 221 

Table 37. — Planting Dates by Vegetable Groups 

Zone Group 1 Group 2 

A Jan. 1 to Feb. 1 Feb. 1 to Feb. 15 

B Feb. 1 to Feb. 15 Feb. 15 to Mar. 1 

C Feb. 15 to Mar. 1 Mar. 1 to Mar. 15 

D Mar. 1 to Mar. 15 Mar. 15 to Apr. 15 

E Mar. 15 to Apr. 15 Apr. 15 to May 1 

F 1 Apr. 15 to May 1 May 1 to May 15 

G 1 May 1 to May 15 May 15 to June 1 

Zone Group 3 Group 4 

A Feb. 15 to Mar. 1 Mar. 1 to Mar. 15 

B Mar. 1 to Mar. 15 Mar. 15 to Apr. 1 

C Mar. 15 to Apr. 1 Apr. 1 to Apr. 15 

D Apr. 1 to May 1 May 1 to May 15 

E May 1 to May 15 May 15 to June 1 

F 1 May 15 to June 1 May 15 to June 15 

G^ xMay 15 to June 15 0) 

Group 1. (May be planted two weeks before the average date of last 
killing frost.) — Early cabbage plants from hotbed or seed-box, radishes, 
collards, onion sets, early smooth peas, kale, early potatoes, turnips, and 
mustard. 

Group 2. (May be planted about the average date of the last killing 
frost.) — Beets, parsnips, carrots, lettuce, salsify, spinach, wrinkled 
peas, cauliflower plants, celery seed, onion seed, parsley, sweet corn, 
and Chinese cabbage. 

Group 3. (Should be planted two weeks after the average date of 
last kilhng frost.) — Snap beans, okra, and tomato plants. 

Group 4. (Cannot be planted until ground is well warmed up; about 
a month after last hard frosts.) — Lima beans, pepper plants, eggplants, 
cucumbers, melons, squash, and sweet potatoes. 

WHITE OR " IRISH '^ POTATOES 

Potatoes rank first as a world food crop on the basis of ac- 
tual pounds produced, although more people depend on rice 
as a staple article in the daily ration. Over 90 per cent of the 
world's production of potatoes is grown in Europe. 

477. Range in the United States.— The potato is the 
most widely distributed crop in this country, although in 
1916 about one-half of the crop was raised in eight states. 

^ For the crops grown. 2 Season too short for this group. 



222 



AGRICULTURAL METEOROLOGY 



In the five years from 1913 to 1917, the states with the highest 
average production, in the order named, were New York, 
Michigan, Wisconsin, Minnesota, and Maine, each of which 
produced over 24,000,000 bushels. 

478. Planting and harvesting. — Figs. 67 and 68 show the 
average date of the beginning of planting and harvesting of 




Fig. 67. — Average dates when the planting of early potatoes begins. 

early potatoes. The number of days from planting to har- 
vesting of the early crop varies from 80 to 100. 

479. Temperature at beginning of planting. — The plant- 
ing of early potatoes generally begins when the mean daily 
temperature in the spring rises to about 45°. The planting 
of early potatoes is nearly one month earlier than the average 
date of the last killing frost in the spring. As it takes less 
than one month for potatoes to come up, the crop is often 
subject to damage by late spring frosts. 

480. Temperature requirements. — The white or ''Irish'' 
potato is a cool-weather crop. It originated in Peru, South 



WEATHER AND MISCELLANEOUS CROPS 223 



America, where the crop is grown at the present time at an ele- 
vation sufficiently high to make the average annual tempera- 
ture about 52°. The mean temperature varies from about 
48° in July to 54° in November. Regions in which the tem- 




FiG. 68. — The beginning of the harvest of early potatoes. 

perature rises to 85° or above for many successive days are 
not adapted to maximum yields. 

Potato production has made the greatest development in 
the United States where the mean annual temperature is be- 
tween 40° and 50° and where the mean temperature of the 
warmest month is not over 70°. The greatest yields to the 
acre are in those states where the mean annual temperature 
is below 45° and where the mean of the warmest month is not 
far from 65°. In the southern states potatoes are a winter 
crop. 

481. Water requirement. — At the Maine Experiment 
Station it was found that it takes about 425 tons of water to 
grow 1 ton of dry matter of potatoes and therefore that a 



224 



AGRICULTURAL METEOROLOGY 



crop of 200 bushels to the acre will require approximately 650 
tons of water. Investigations in northeastern Colorado as 
well as in Utah determined that the weight of water absorbed 
during the growth of potatoes to the weight of dry matter 
produced was close to 450. The weight of water falhng on 1 
acre of land to the depth of 1 inch is 112.7 tons. Hence if the 
growing plants could use all of the water, it would require a 
rainfall between 5 and 6 inches between planting and harvest- 
ing to raise a 200-bushel crop. 

The actual record of the rainfall in much of the country be- 
tween planting and harvesting of the early potato crop is be- 
tween 8 and 10 inches. 

482. Distribution of water. — Experiments show that 
potatoes need a uniform distribution of water. A five-year 
test in Utah demonstrated that 1 inch of water weekly, or a 
total of 12.8 inches during the season gave a higher yield than 
any other treatment. When but one irrigation was given, 
the best results were obtained if applied when the potatoes 
were in full bloom. 

483. Weather and potatoes in Ohio. — The following table 
shows the effect of rainfall or temperature on the yield of po- 
tatoes in Ohio: 



Table 38. — Correlation Between the Rainfall and Tempera- 
ture AND THE Yield of Potatoes in Ohio, 1860 to 1914 

Period Rainfall Temperature 

Correlation Probable Correlation Probable 

coefficient error coefficient error 

AprU -0.21 ±0.09 — 

May 0.06 ±0.10 —0.10 ±0.09 

June 0.10 ±0.09 —0.22 ±0.09 

July 0.33 ±0.08 —0.51 ±0.07 

August 0.22 ±0.09 —0.31 ±0.08 

September —0.13 ±0.09 —0.21 ±0.09 

October 0.07 ±0.10 —0.11 ±0.09 

June, July comb _ —0.50 ±0.07 

July, August comb 0.37 ±0.08 —0.50 ±0.07 

June, July, Aug. comb — ■ —0.49 ±0.07 

484. Effect of varying rainfall. — Remembering that the 
correlation should be at least three times the probable error 
to indicate an appreciable effect and that if it is six times the 



WEATHER AND MISCELLANEOUS CROPS 225 

probable error there is plainly considerable relation shown, it 
will be seen at once that the rainfall in Ohio is not a dominat- 
ing factor in varying the yield of potatoes, when considered 
for calendar months. July and July and August combined 
show a fairly high relation, but this is not high enough to be 
important. 

485. Effect of temperature. — The last two columns of 
Table 38, however, show that the yield is affected by the 
temperature variation and also that the summer should be 
cool. 

486. July most important. — The highest correlation be- 
tween the July temperature and potato yield is —0.51 for 
July and this is more than seven times the probable error. 
This indicates that July should be cooler than normal in Ohio 
for the best potato yields. Fig. 14 shows graphically the re- 
lation between the mean temperature in July and the yield 
of potatoes in Ohio. It makes plain that cool weather is most 
desirable, while a warm July is nearly always followed by a 
poor yield. If only those years are considered when the tem- 
perature variation is 1 degree or more from the normal it is 
fouLd that when July is warm the probability of a good potato 
crop is only 12 per cent, and when July is cool the probabil- 
ity of the potato crop being greater than the average is 77 per 
cent. 

487. Some temperature and yield comparisons. — By tab- 
ulating the years by variations in mean temperature for the 
month of July in Ohio, some interesting changes are shown in 
the yield figures, as indicated in the following table : 

Table 39. — Variations in Yield of Potatoes in Ohio with Varying 
Average Temperatures in July, 1860 to 1914 

July mean temperature (Deg. F.) Potato yield (bushels) 

Groups Average Years Average 

Below 72.6 71.5 16 86.6 

72.6 to 73.5 73.1 13 80.0 

73.6 to 74.5 74.1 11 76.5 

Above 74.5 76.3 15 67.7 

This table shows an average decrease in the yield of pota- 
toes in Ohio of 6.3 bushels to the acre with each increase of 
1.6° in the average temperature for the month of July. Tak- 



226 AGRICULTURAL METEOROLOGY 

ing into account the acreage devoted to potatoes in this state 
and the average farm price during the past ten years, it is 
found that for every increase in the average temperature for 
the month of July of 1.6°, the talue of the potato crop in Ohio 
has been reduced $4.03 an acre, or a total of 1,096,200 bushels, 
worth $701,568. 

There were sixteen years during the period when the tem- 
perature averaged below 72.6°, and fifteen years when it aver- 
aged above 74.5°, and by tabulating the yield figures during 
these years an average variation in the yield of 18.9 bushels 
to the acre is found, or an average of 3,288,600 bushels, worth 
$2,104,704. 

488. Combined effect of temperature and rain, Ohio. — 
In Fig. 69 the combined effect of the temperature and rain- 
fall for the month of July is indicated. The diagram shows 
that there were thirteen years during the fifty-six when July 
in Ohio was warm and wet, and that in these years there were 
ten with a yield below the normal and three with a yield above 
the normal. This indicates that when July is warm and wet, 
the probability of a good potato yield in Ohio is only 23 per 
cent. When July is warm and dry, the diagram shows ten 
years with the yield below the normal and four with the 
yield above the normal. This indicates that when July is 
warm and dry, the probability of a potato yield above the 
normal is only 29 per cent. When July has been cool and dry, 
there have been seven years with a yield above the normal 
and seven years below the normal, indicating that the prob- 
ability of a good potato crop with these conditions is just 50 
per cent. When it has been cold and wet, however, the chart 
shows only three years with a yield below the normal and 
twelve with a yield better than the average. This indicates 
a probability of 80 per cent that the yield will be above the 
normal in Ohio if July is cool and wet. 

489. In New Jersey. — In the state of New Jersey in, the 
past thirty-three years the yield of potatoes has been below 
the normal every year but two, v/hen the average temperature 
in July has been 1 degree or more above the normal. And 
when the mean temperature for July has been below the nor- 
mal, the yield has been greater than the average every year 
but two. There have been eleven years when the tempera- 
ture in July has averaged 1 degree or more above the normal 



WEATHER AND MISCELLANEOUS CROPS 227 



and the average yield of potatoes for those years has been 12 
bushels to the acre less than the normal. There have been 
twelve years when the temperature has averaged 1 degree 
or more lower than the normal and during these years the po- 
tato yield has averaged 13 bushels to the acre greater than 
the normal. 

This makes an average difference of 25 bushels of potatoes 
to the acre in New Jersey depending on whether the month 
of July is appreciably warmer or cooler than the average. 



+ 7 


3 -2 -1 INCHES +1 +2 +3 -t-A 




+ 6 
+ 5 
<-4 
+ 3 
+ 2 

+ 1 

i2 

-1 
-2 

-3 

-4 
-5 












1 




























J 
< 




. 






















- 









- 












WARM a DRY 




* 


' 




- 




VA^ARM 


a WET 














+ 


- 






_ 


. 


















■4- 


- 




















•»■»' 


ORMA 






+ 


+■ 


+ 


t 






■J- 


ZMPE^ 


ATUR 


e 








- - 


+ -+ 


- 


f 


+ 












_ 


■ 


+ 




+ 


w* 




+ 


+ 






















* i 






_ 




y 








< 


•OOL 


a DRY 




•f 


z 








d 


OOL i 


it wet" 

















*i 














AJ. 





+ VICLD ABOVE NORMAL 



YIELD BELOW NORMAL 



Fig. 



69. — The combined effect of the July temperature and rainfall 
on the yield of potatoes in Ohio, 1860 to 1915. 



Taking the figures for 1916 as a basis for calculation, this 
means a difference in the total potato yield of 2,125,000 bush- 
els, worth $1,290,760. The average increase in the value of 
the potato crop an acre in New Jersey is thus close to $21, if 
July is cool over what it is when July is very warm. 

490. In Wisconsin. — A correlation between the July tem- 
perature and the yield of potatoes in Wisconsin for twenty- 
seven years gives a correlation coefficient of — 0.39, probable 
error ±0.11. 

491. In Michigan. — The correlation coefficient between 
the July temperature and yield of potatoes in Michigan cov- 



228 AGRICULTURAL METEOROLOGY 

ering a period of twenty-eight years is — 0.54 or five times 
the probable error. 

492. In Licking County, Ohio. — The following tabulation 
gives the correlation between the temperature and the yield 
of potatoes in Licking County, Ohio, for the period from 1860 
to 1913: 

Table 40. — Correlation between Temperature and Yield of 
Potatoes in Licking County, Ohio 

Period Correlation coefficient Probable error 

April —0.01 ±0.09 

May +0.08 ±0.09 

June —0.29 ±0.08 

July —0.36 ±0.08 

August —0.28 ±0.09 

September —0.23 ±0.09 

October —0.15 ±0.09 

June, July combined —0.44 ±0.07 

July and August combined —0.44 ±0.07 

August and September combined. . . — 0. 15 ±0.09 

It will be seen that the correlation coefficient for June and 
July combined and for July and August combined is almost 
six times the probable error. 

493. In Portage County, Ohio. — This is an important 
potato-growing county, but a correlation of the weather of 
different months and the yield of potatoes in that county 
covering the period from 1860 to 1913 gives very low correla- 
tion coefficients. This is probably due to the fact that the 
blooming period comes about the middle of August and that 
warm weather is needed before blooming and cool after bloom- 
ing; thus the effect is neutralized. 

494. Critical period of growth. — The tables following give 
phenological dates and data in connection with the growth 
of potatoes at Wauseon, Ohio, kept by Thomas Mikesell. 



WEATHER AND MISCELLANEOUS CROPS 229 



Table 41. — Phenological Dates and Data for Growth of Early 
Potatoes at Wauseon, Ohio, 1883 to 1912, by Thomas Mike- 
sell 

(Lat., 41° 35' N., long., 84° 07' E.; alt., 780 feet A. M. S. L.) 















Per 








Date 




Date 




cent 




Year 


Date 


above 


Date in 


ready 


Date 


of Quality 




planted 


ground 


bloom 


for use 


ripe 


good 
crop 


of 
crop 


1883 1 


April 12 


May 8 


June 10 


June 30 


Aug. 20 


. . . 




1884 


21 


14 


18 


July 2 


July 30 







1885 


23 


19 


25 


9 


31 







1886 


22 


9 


12 


June 24 


July 20 


85 


Good 


1887 


26 


11 


18 


30 


25 


100 


Good 


1888 


23 


18 


20 


July 10 


Aug. 8 


70 


Good 


1889 


22 


11 


21 


June 27 


15 


95 


Good 


1890 


25 


13 


14 


22 


July 28 


50 


Fair 


1891 


24 


11 


17 


June 29 


Aug. 7 


95 


Good 


1892 


28 


14 


20 


July 1 


15 


90 


Good 


1893 


24 


15 


16 


5 


1 


60 


Good 


1894 


17 


1 


8 


June 25 


1 


60 


Good 


1895 


27 


7 


17 


July 10 


20 


60 


Good 


1896 


May 1 


12 


14 


June 19 


8 


100 


Good 


1897 


6 


20 


25 


July 10 


July 28 


60 


Good 


1898 


21 


30 


20 


30 


Aug. 20 




.... 


1899 


April 26 


6 


10 


June 20 


5 


80 


Good 


1900 


28 














1901 


17 




June 20 











1902 


21 




8 


June 23 








1903 






May 28 










1904 


Mav 5 


May 17 


June 20 




Sept.' 12 


75 


Good 


1905 


4 


10 


6 


June 27 


Aug. 25 


80 


Good 


1906 


April 24 


10 


11 


July 3 


Sept. 1 


80 


Good 


1907 


Mav 4 


14 


18 


7 


Aug. 20 


45 


Good 


1908 


April 22 


10 


8 


12 


1 


50 


Good 


1909 


May 5 


12 


8 


3 


5 


60 


Good 


1910 


April 8 


8 


18 


10 


20 


85 


Good 


1911 


May 4 


25 


24 


8 


July 28 


40 


Fair 


1912 


April 16 


9 


16 


June 28 


July 25 


75 


G^d 


Average April 26 


May 13 


June 15 


July 2 


Aug. 9 


72 






iData for the years 1883 to 1901, inclusive, apply to MikeselFs 
own farm; data for 1902 to 1912 apply to certain nearby fields the 
same field being used for the entire season. 



Table 42. — Constants During the Growth of Potatoes at 
Wauseon, Fulton Co., Ohio, 1883 to 1912 

Total effective temperature 
Time {above 43° F) Total rainfall 



'^ 



1 1 



^ J § ^ J ^ J 

l-s^ ^|5 ^l-s ^ 

-§ ns ^ g -f^ -e ^ S -i: -i - 



e s 



o o s -.s. o o 



1 



■l ^ I I I 'I ^ I ^ 1 I I 1 

ooooocso o ooo o o 

^S- -J- ^J- r^ r^ r^ ^^ r^ r^ ^5- r^ ^^ ^5^ 

Year Ds. Ds. Ds. Ds. Ds. F F F F In. In. In. In. 

1883 26 33 53 71 130 215 502 1,737 2,454 1.0 6.7 10.8 18.5 

1884 23 35 50 42 100 272 764 1,163 2,199 2.6 2.9 5.0 10.5 

1885 26 37 51 36 99 244 836 1,090 2,170 3.4 6.9 3.2 13.5 

1886 17 34 46 38 89 242 630 1,036 1,908 1.4 2.3 1.8 5.5 

1887 15 38 50 37 90 243 906 1,311 2,460 1.3 4.7 4.4 10.4 

1888 25 33 53 47 105 269 731 1,418 2,418 2.0 2.3 4.0 8.3 

1889 19 41 47 55 115 273 707 1,455 2,435 0.1 11.4 6.8 18.3 

1890 18 32 40 44 94 143 680 1,177 2,000 5.5 1.6 4.0 11.1 

1891 17 37 49 51 105 200 720 1,349 2,269 0.8 3.2 4.4 8.4 

1892 16 37 48 56 109 171 746 1,617 2,534 7.4 10.4 6.1 23.9 

1893 21 32 51 46 99 153 675 1,378 2,206 5.2 3.9 5.2 14.3 

1894 14 38 55 54 106 183 553 1,738 2,474 2.4 4.0 3.1 9.5 

1895 10 41 64 64 115 240 868 1,976 3,084 1.2 1.8 2.5 5.5 

1896 11 33 38 55 99 285 749 1,617 2,651 0.7 4.9 13.7 19.3 

1897 14 36 51 33 83 234 678 1,031 1,943 2.0 3.3 4.6 9.9 

1898 9 30 61 52 91 188 801 1,570 2,559 0.7 3.6 6.7 11.0 

1899 11 35 45 56 102 275 729 1,653 2,647 1.0 4.1 5.2 10.3 
1900-1903 

1904 12 34 .. 83 129 148 687 2,075 2,910 0.6 3.3 8.0 11.9 

1905 6 27 48 80 114 64 422 2,178 2,664 1.0 6.8 9.5 17.3 

1906 16 32 54 82 130 151 718 2,280 3,149 0.9 3.0 10.2 14.1 

1907 10 35 54 63 108 103 480 1,717 2,400 0.5 5.9 6.3 12.7 

1908 18 29 63 54 101 124 665 1,507 2,296 1.8 4.9 7.7 14.4 

1909 7 27 52 58 92 76 495 1,532 2,103 2.4 3.5 7.6 13.5 

1910 30 41 63 63 134 202 593 1,841 2,636 5.8 2.6 6.4 14.8 

1911 21 30 44 34 85 505 802 963 2,270 0.5 3.9 6.5 10.9 

1912 23 38 50 39 100 223 723 1,062 2,008 1.7 6.1 1.7 9.5 
Aver. 17 34 50 55 106 209 687 1,518 2,414 2.1 4.5 6.0 12.6 

230 



WEATHER AND MISCELLANEOUS CROPS 231 

A correlation between the thermal constants and rainfall 
and the potato yield gives the following: 

Table 43. — Correlation Between Thermal Constants and 
Potato Yield, Wauseon, Ohio, 1883 to 1912 

Correlation Probable 

Period coefficient error 

From date of planting to date above ground. . 0.03 ±0. 12 

From date above ground to date of bloom .... . 24 =i= . 12 

From date of bloom to date ripe 0. 16 ±0. 12 

From date planted to date ripe 0.25 ±0.11 

For 10 days before blooming 0. 17 ±0. 12 

For 10 days after blooming -0.30 ±0. 11 

Table 44. — Correlation Between Rainfall and Potato Yield, 
Wauseon, Ohio, 1883 to 1912 

Correlation Probable 

Period coefficient error 

For 10 days before planting 0.02 ±0. 12 

From date planted to date above ground —0.06 ±0. 12 

From date above ground to date in bloom. ... 0.33 ±0. 11 

From date in bloom to date ripe 0.18 ±0.12 

For 10 days before blooming 0.09 ±0. 12 

For 10 days after blooming —0.07 ±0. 12 

From these tables it is evident that cool weather is desir- 
able during the ten days after blooming and that it should 
be fairly wet before blooming. 

495. Correlation for short periods. — A correlation of the 
temperature and rainfall with the potato yield in three coun- 
ties in central Ohio for the period from 1891 to 1910 gives the 
following: 



232 



AGRICULTURAL METEOROLOGY 



Table 45. — Correlation Between Weather for 10-day Periods 
AND THE Yield of Potatoes in Central Ohio for the Years 
1891 TO 1910 





Rainfall 


Temperature 


Period 


Correlation 


Probable 


Correlation Probable 




coefficient 


error 


coefficient error 


June 1 tolO. . . 


0.29 


±0.12 


-0.12 ±0.13 


June 11 " 20. . . 


0.32 


±0.12 


-0.17 ±0.13 


June 21 "30... 


0.16 


±0.13 


-0.28 ±0.12 


July 1 " 10. . . 


0.4S 


±0.10 


-0.44 ±0.11 


July 11 "20... 


. . -0.29 


±0.12 


-0.33 ±0.12 


Julv 21 " 31 . . . 


. . -0.12 


±0.13 


-0.33 ±0.12 


Aug. 1 "10. .. 


0.06 


±0.13 


-0.23 ±0.13 


Aug. 11 "20... 


0.37 


±0.11 


-0.36 ±0.11 


Aug. 21 "31... 


. . -0.26 


±0.12 


-0.38 ±0.11 



Table 46. — Correlation of Weather for 20-day Periods with 
Potato Yield in Central Ohio, 1891 to 1910 

Rainfall 
Period Correlation 

coefficient 

June 1 to 20 0.48 

June 11 "30 0.30 

June 21 " July 10. 0.44 
July 1 '' 20 0.03 

July 11 "31 -0.23 

July 21 " Aug. 10. -0.08 

Aug. 1 "20 0.29 

Aug. 11 "31 0.22 



u 


Temperature 


Probable 


Correlation Probable 


error 


coefficient error 


±0.10 


-0.19 ±0.13 


±0.12 


-0.27 ±0.12 


±0.11 


-0.61 ±0.09 


±0.13 


-0.54 ±0.10 


±0.12 


-0.41 ±0.11 


±0.13 


-0.42 ±0.11 


±0.12 


-0.36 ±0.11 


±0.12 


-0.43 ±0.11 



Table 47. — Correlation of Weather for 30-day Periods with 
Potato Yield in Central Ohio, 1891 to 1910 





Rainj 


all 


Temperature 


Period 


Correlation 


Probable 


Correlation Probabl 




coefficient 


error 


coefficient error 


June lto30 


0.42 


±0.11 


-0.33 ±0.12 


June 11 " July 10. 


0.58 


±0.09 


-0.53 ±0.10 


June 21 " July 20. 


0.26 


±0.12 


-0.61 ±0.09 


July 1 "31 


0.002 


±0.13 


-0.57 ±0.09 


July 11 " Aug. 10. 


-0.20 


±0.13 


-0.51 ±0.10 


July 21 " Aug. 20. 


0.19 


±0.13 


-0.49 ±0.10 


Aug. 1 " 31 


0.11 


±0.13 


-0.35 ±0.11 



WEATHER AND MISCELLANEOUS CROPS 233 

Table 48. — 'Correlation of Weather for 40-day Periods with 
Potato Yield in Central Ohio, 1891 to 1910 





Rainfall 


Temperature 


Period 


Correlation 


Probable 


Con-elation Probable 




coefficient 


error 


coefficient error 


June 1 to July 10. 


0.59 


±0.09 


-0.58 ±0.09 


June 11 " July 20. 


0.35 


=«=0.11 


-0.58 ±0.09 


June 21 " July 31. 


0.09 


±0.13 


-0.62 ±0.09 


July 1 " Aug. 10. 


0.02 


±0.13 


-0.63 ±0.09 


July 11 " Aug. 20. 


0.02 


±0.13 


-0.54 ±0.10 


July 21 '' Aug. 31. 


0.06 


±0.13 


-0.51 ±0.10 


Table 49. — Correlation of Weather fob 


I 50-DAY Periods with 


Potato Yield in Central Ohio, 


1891 to 1910 




Rainfall 


Temperature 


Period 


Correlation 


Probable 


Correlation Probable 




coefficient 


error 


coefficient error 


June 1 to July 20. 


0.44 


±0.11 


-0.58 ±0.09 


June 11 " July 31. 


0.20 


±0.13 


-0.54 ±0.10 


June 21 " Aug. 10. 


0.09 


±0.13 


-0.65 ±0.08 


July 1 " Aug. 20. 


0.17 


±0.13 


-0.67 ±0.08 


July 11 " Aug. 31. 


-0.05 


±0.13 


-0.52 ±0.10 



These tables show that the period covering the first ten 
days in July is a critical one for potatoes in central Ohio when 
it should be cool and wet. The correlation coefficient for tem- 
perature is four times the probable error and for rainfall 
nearly five times the probable error. 

The most critical twenty-day period is from June 21 to 
July 10; the most important thirty days from June 11 to July 
10 for rainfall and June 21 to July 20 for temperature; the 
most important forty daj-s from June 1 to July 10 for rainfall 
and from July 1 to August 10 for temperature; and the most 
important fifty days from June 1 to July 20 for rainfall and 
from July 1 to August 20 for temperature. 

The temperature correlation emphasizes the previous de- 
terminations that relatively cool weather is needed for pota- 
toes. 

496. Diseases of potato plants. — The foliage of the 
potato plant is particularly subject to diseases which are af- 
fected by weather conditions to a marked degree. Early 
blight, and the Fusarium dry-rot are dry-weather diseases, 
while late blight develops in wet and cool weather in some dis- 



234 AGRICULTURAL METEOROLOGY 

tricts and in wet and hot weather in others. Sun-scald oc- 
curs when bright and hot weather follows suddenly a moist 
and cloudy period. 

Other diseases such as brown-rot, rosette, potato-wilt, and 
dry-end rot affect the foliage in particular sections of the 
country, and it seems probable that a further study of these 
will show that most of them are more or less severe under cer- 
tain weather conditions. 

497. Late blight.— The so-called ''late blight" of potatoes 
is the most serious of all potato diseases and is due to the fun- 
gus Phytopthora infestans. The potato rot resulting from 
this disease caused very great loss in eastern North America 
in 1842, 1845, and 1874, and there was a general outbreak in 
New England and New York in 1901, 1902, and 1903. In 
1845 the disease spread through Great Britain, Ireland, and 
Belgium, and the terrible Irish famine of that year was due 
to the almost total loss of the potato crop of Ireland from this 
disease during the preceding summer. 

This disease is undoubtedly favored by moist weather. 
Rainfall apparently has much to do with the spread of the dis- 
ease, particularly if heavy rain is followed by cloudy weather 
and still air, when the moisture will cling to the leaves for a 
long time. If the rainfall is followed by clear skies and suffi- 
cient wind to evaporate the moisture rapidly from the potato 
leaves, then the disease will be checked. 

498. Effect of temperature on late blight. — Writers in 
some parts of the country state that late blight will develop 
with a spell of warm, moist, "muggy" weather, while in other 
sections it will be noted that a serious outbreak of late blight 
has followed a period of cool moist weather. 

In Bulletin 245 of the United States Bureau of Plant In- 
dustry, the following statement is made as to the effect of 
temperature on Phytopthora infestans: 

Exposing test-tube cultures for 10 minutes at temperatures up to 40° 
C. did not prevent the later development of the fungus; beyond this 
temperature inhibition resulted. Where cultures were held at constant 
temperatures the best growths resulted between 1G° and 19° C. (60.8° 
and 66.2° F.) Below 16° C, the growth was slower and below 5° C. 
(41.0° F.) it was wholly inhibited. At and above 23° C, (73.4° F.) the 
growth was inhibited, with no sporulation above 25° C. (77° F.) and no 
vegetative growth at or above 30° (86° F.). 



WEATHER AND MISCELLANEOUS CROPS 235 

A. D. Selby, in the " Ohio NaturaUst" for February, 1907, 
quoting from Scribner says: ''A temperature ranging from 
65° to 75° F. produces conditions favorable for the disease;" 
and quoting from Galloway, ^'A daily mean or normal tem- 
perature of from 72° to 74° for any considerable time, accom- 
panied by moist weather, furnishes the best conditions for the 
spread of the disease." 

499. Most favorable temperatures. — It should be noted 
that while the authors quoted above do not agree as to the 




-Average highest mean daily temperature during the 
warmest part of the season. 



most favorable temperatures for the spread of late blight, in 
one instance the writer refers to tests made under constant 
temperatures while the other two refer to mean daily temper- 
atures, when the temperature would be higher than the opti- 
mum in the daytime and lower in the night. 

It is probable, therefore, that the most favorable open-air 
temperature condition is when the mean daily temperature 
is between 70° and 74°. Also that the development of the 
disease is checked if the mean daily temperature is above 75° 
for a few days, and that the spores are killed at a temperature 
of 77° to 80°. 



236 AGRICULTURAL METEOROLOGY 

500. Temperature terms relative. — In Fig. 70 there has 
been entered the highest mean daily temperature during the 
warmest part of the year at each of the Weather Bureau sta- 
tions. Isothermal lines have been drawn for each 5 degrees. 
This chart shows that in extreme northern parts of the coun- 
try and in the higher parts of the Rocky Mountain states, 
the mean summer temperature is generally too low for the 
best development of late blight in potatoes and that practi- 
cally all of the central and southern districts are too warm for 
the disease to get a foothold. This makes plain also why in 
Maine late blight is a disease of '^warm" moist weather, while 
in Ohio it is spoken of as a disease of "cool" moist summers. 
An inspection of the yearly temperature records would show 
that north of this normal temperature line of 70°, there are 
seasons or periods when the temperature is high enough to 
cause an outbreak of the late blight, and that even south of 
the line of 75° a season might be cool enough to cause loss to 
the potato crop. The critical district would be along the line 
of 70°, as shown on this chart. 

501. Time of development. — It must be remembered 
that in the southern part of this critical area it would take 
more than a few weeks of cool weather to develop the disease 
and that even one cool season would hardly do it; but that 
with a series of cool summers it might become sufficiently de- 
veloped to cause serious damage, so that even with a cool 
moist sunimer which is favorable for the growth of potatoes 
there might result a very poor yield, due to loss by late blight. 
One warm and dry season, although unfavorable for the yield 
of potatoes, would kill out the Phytopthora so effectually that 
it would take another series of cool years for it to become 
again established. 

HAY AND FORAGE CROPS 

The acreage of hay and forage crops in the United States 
is second only to corn. Their distribution depends on a com- 
bination of climatic and economic factors. The area with the 
highest relative acreage lies from eastern Kansas, Nebraska, 
and South Dakota eastward to New England. 

502. Climatic factors. — This region has a generous snow- 
fall and generally a good snow-cover during cold winter 



WEATHER AND MISCELLANEOUS CROPS 237 

weather, the summer rainfall is well distributed, and, in the 
northern part of the region, the summers are cool. 

503. Weather and yield of hay. — A study made several 
years ago covering sixteen states in the northeastern part of 



^ t '5 fe fe S 8; 5 8; 5 a g S! § 



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•. 


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Fig. 71. — Relation between the rainfall in May and the 
yield of hay (not including clover) in Ohio, 1858 to 
1909. 



the country showed that the rainfall for May had a large in- 
fluence on the yield of hay. This and the further fact that 
the price of hay is influenced by the yield aided materially in 
a decision of the Inter-State Commerce Commissioners in a 
celebrated hay-rate case involving several million dollars. It 
has been stated that in order to produce a ton of dry hay on 



238 AGRICULTURAL METEOROLOGY 

an acre of land, it is necessary that the growing grass pump 
up from that acre approximately 500 tons of water. 

504. Hay in Ohio. — A comparison of the rainfall in May 
and the yield of hay in Ohio for the years from 1858 to 1909, 
gave a correlation of +0.49 with a probable error of ±0.07. 
The correlation for April and May was the next highest or 
+0.45, probable error =fc0.07. 

Fig. 71 gives a dot chart showing the relation between the 
rainfall in May and the yield of hay in Ohio. This indicates 
that a May rainfall of more than 1 inch above the normal, is 
always followed by a yield of hay above the normal. When 
the rainfall has been more than 1 inch below the normal, the 
yield has been below the normal eleven times and above five 
times. 

It is plain, therefore, that other influences besides the May 
rain affect the yield, especially when the rainfall is light, as a 
large yield is frequently harvested following a comparatively 
dry May. 

505. Hay in New York. — A recent study covering twenty- 
three years, from 1888 to 1911, showed that a normal rainfall 
is most favorable in New York. In nine years out of twenty- 
three when the rain was within 2 per cent of the normal, the 
yield was over 8 per cent above the average. That this crop 
does not appear to utilize much more than the normal 
amount of moisture is indicated by the fact that in seven 
years when the rainfall was 27 per cent above normal, the 
yield was only 5 per cent above the average. On the other 
hand, a slight deficiency resulted in a marked decline in the 
yield. In five years when the deficiency was marked, the 
yield was 32 per cent below the average. 

506. Hay in Wisconsin. — The correlation between weather 
and the yield of hay in Wisconsin for twenty-seven years is 
indicated in the following: 

Table 50. — Correlation between Weather and Yield of Hay in 

Wisconsin 

Rainfall Temperature 

Month Correlation Probable Correlation Probable 

coefficient error coefficient error 

April +0.05 -0.24 ±0.12 

May +0.38 ±0.11 -0.11 

June +0.25 ±0.12 -0.58 ±0.09 



WEATHER AND MISCELLANEOUS CROPS 239 

507. Hay in other states. — The following shows the cor- 
relation of the rainfall for April and May with the yield of 
hay for different states: 

Table 51. — Correlation of Rainfall for April and May with 
Yield of Hay 

Rainfall 
April May 

State Years Correlation Probable Correlation Probable 

coefficient error coefficient error 

California 19 

Iowa 26 

Nebraska 40 

New Mexico 24 

New York 26 

North Dakota. ... 24 

Oklahoma 14 

Tennessee 33 

Washington 26 

Wisconsin 25 

508. June rain. — Charts of the relation between the June 
rain and the hay jdeld indicate that the later rain has consid- 
erable effect on the yield in North Dakota, but not in Wiscon- 
sin or any of the southern or western states given in the above 
table. In New Jersey and in more southern districts, it is 
probable that the April or even March weather may have a 
greater influence than that of later months. 

509. Alfalfa requires more water than most crops, but 
the ability of the plant to send its roots to great depths makes 
it very drought-resistant and a valuable croj:) for semi-arid 
regions. It is found that alfalfa thrives best where the water- 
table is at a fairly uniform height. 

510. Alfalfa and temperature. — Alfalfa is able to with- 
stand high temperatures when the air is drj^, but if accom- 
panied by humid air high temperatures are injurious. If a 
hard freeze occurs soon after the plants come up, especially 
when the soil is damp, a large proportion may be killed. Al- 
falfa is liable to be winter-killed with freezing and thawing of 
the ground without snov/-cover. An ice-sheet is very dam- 
aging. 



+0.12 


=^0.13 


-0.017 


±0.19 


+0.16 


±0.13 


+0.56 


±0.09 


+0.10 


±0.11 


+0.45 


±o.oa 


+0.07 


±0.13 


+0.18 


±0.13 


+0.44 
+0.12 


±0.11 
±0.13 


+0.003 
+0.35 




±0.12 


+0.85 


±0.05 


+0.28 


±0.15 


-0.18 


±0.11 


+0.32 


±0.10 


-0.58 


±0.08 


+0.07 


±0.13 


-0.02 


±0.13 


+0.44 


±0.11 



240 AGRICULTURAL METEOROLOGY 

511. Alfalfa in Nevada. — Alfalfa develops the highest 
food values when there is a high percentage of sunshine and 
the days are moderately warm and the nights cool. Enough 
moisture is needed to keep the soil in good condition, but too 
much cloudy weather is detrimental to the growth of slender 
stalks and a large number of leaves. Hot days and warm 
nights with much moisture cause the plant to develop a 
woody stock and fewer leaves. Plenty of sunshine, moder- 
ately warm days and cool nights cause alfalfa to develop more 
chlorophyll, which gives the plant more nutriment. 

512. Curing alfalfa. — As this plant cures slowly, a good 
crop is frequently greatly damaged in harvesting in the humid 
sections of the country where rains are frequent. The im- 
portance of cutting during good weather has led to the es- 
tablishment of an alfalfa fair weather warning service by the 
United States Weather Bureau. Forecasts of three or four 
days or more of fair weather are made and widely distributed 
in the principal alfalfa-growing districts during the harvest- 
ing season. 

513. Alfalfa seed and frost. — Alfalfa seed ripens unevenly 
and the best plants, setting burrs heavily well down on the 
lower stems, will contain many green burrs, yellow burrs 
(turning ripe), and brown or ripe burrs at the same time. The 
yellow stage of the burr endures for about one week in Utah 
under ordinary conditions during which time the seed, if cut, 
will ripen from sustenance in the parent stem, if in good con- 
dition. The seed-growers estimate that near harvest time 
the crop increases in value about $5 an acre each twenty-four 
hours. For this reason it is desired that the crop be allowed 
to stand as long as unripe seeds remain. A light frost or a 
temperature of 31° or 32° in the alfalfa foliage is harmless to 
the brown burrs, but will injure the exposed yellow burrs and 
some of the green burrs. A temperature of 26° to 28° in the 
foliage will cause heavy damage to both yellow and green 
heads, the injury varying with the amount of leaf foliage and 
the proportion of these immature burrs. The effect of the 
frost is to blacken the seed, making it less salable and prob- 
ably less viable. 

514. Alfalfa seed warning service, Utah. — When the frost 
warning service is in operation, the seed is left standing 
until a warning is received. On receipt of the warning, as 



WEATHER AND MISCELLANEOUS CROPS 241 

many mowers as are available are sent into the field and cut- 
ting is sometimes continued on moonlight nights well into the 
night. When cut, whether left flat or raked into windrows, 
comparatively little of the seed will be damaged. Tens of 
thousands of dollars worth of seed will be saved in this way 
on receipt of a frost warning. 

515. Clover thrives best in a humid climate, and where 
the winter and summer temperatures are not extreme. It is 
said that white clover will withstand greater temperature ex- 
tremes than either red or alsike. Crimson clover is less re- 
sistant to low temperatures than the other common clovers. 
Sweet clover thrives best in rather humid regions, but also 
grows well in semi-arid districts. This crop is adapted to a 
wide range in temperature. 

516. Weather and clover. — A correlation between the 
weather and yield of clover in Ohio covering a period of twelve 
years gave the following: 



Table 52. — Correlation between Weather and Yield of Clover 

IN Ohio 



District 

Franklin Co. 
Ohio 
Ohio 
Ohio 

Franklin Co. 
Ohio 

Franklin Co. 
Ohio 
Franklin Co, 



Period 
Winter 

Jan, 

March 

<( 

April 

May 
May 



Rain 
Correlation Probable 
coefficient error 



+0.50 
+0.12 

+0.38 



±0.14 



=0.16 



Temperature 
Correlation Probable 
coefficient 



-0.43 
-0.32 
-0.38 
+0.75 
+0.14 
-0.51 
-0.28 
-0.41 



error 
to. 15 
to. 17 
to. 16 
to. 08 

to. 14 



517. Clover in Ohio. — A more extensive study of weather 
and clover yield in Ohio for the period from 1864 to 1913 gave 
correlations as follows: 



242 AGRICULTURAL METEOROLOGY 

Table 53. — Correlation between Weather and Yield of Clover 
IN Ohio, 1864-1913 

Rainfall 

Period Correlation Probable 

coefficient error 

April +0.15 =^=0.09 

May +0.32 ±0.09 

June -0.09 

July +0.08 

It is probable that the weather during the winter has a 
greater effect on the yield of clover than the rainfall of the 
spring or summer. 

518. Clover seed. — Dry weather is unfavorable for clover, 
but favorable for the seed crop because fertilization by bees 
can go on better. The pollen grains of red clover are partic- 
ularly sensitive to moisture, hence there is little effective pol- 
lination when the flowers are wet. The time between pollina- 
tion and fertilization varies with the temperature. In July it is 
about eighteen hours and in October, thirty-five to fifty hours. 

519. Timothy thrives best in a moist cool climate. It is 
unable to endure hot and dry summer weather and is not 
grown south of latitude 36° except at high elevations. The 
greatest number of flowers bloom in the early morning hours, 
from about midnight until the time of or soon after sunrise. 
The number of flowers that bloom each day, and also to some 
extent the time of blooming, are affected by weather condi- 
tions, especially temperature. Clear weather and a minimum 
temperature of about 60° or above are most favorable. Tim- 
othy flowers have not been observed blooming when the tem- 
perature during the preceding twenty-four hours was as low 
as 50° F. 

520. Millet needs a fairly large amount of rain and must 
have warm weather during the growing season. It was found 
in Russia that between the formation of the leaves and the 
appearance of the flowers, temperature is the most important 
factor and should not fall below 18° C. (64.4° F.). Severe 
cold delays the appearance of the blossoms. The period be- 
tween the flowering and the ripening of the grain was most 
critical for rainfall. Millet has a comparatively shallow root 
system and therefore can well use light rains. 



WEATHER AND MISCELLANEOUS CROPS 243 

521. Sorgo has a much deeper root system than millet 
and can use water from a lower depth. This crop can cease 
to grow during a dry spell and when a good rain comes will 
revive and make a rapid growth. Both crops have a very low 
water requirement and mature quickly. 

522. Cowpeas are adapted to those sections with warm 
summers. 

523. Rape grows best under cool and moist conditions. 

SUGAR PRODUCTS 

In the United States, sugar is produced from sugar-cane 
and sugar-beets, and to a limited extent, from maple sap. 
Large quantities of sirup are made from maple sap in the 
northeastern states and from sweet sorghums in the central 
and southern states. 

524. Sugar-cane is a tropical plant and requires high 
temperatures and a large and constant supply of moisture for 
its best development. The length of time from planting to 
tasseling (the end of growth) varies in Hawaii from eighteen 
months to two and one-half years. The plant is damaged by 
cold weather, hence in Louisiana cane must be harvested in 
an immature state, with the result that the yield of cane aver- 
ages much less than in Hawaii. 

525. Water requirements of sugar-cane. — The optimum 
rainfall for a crop in Louisiana is about 60 inches. Li the 
West Indies the rainfall of July and August and September 
decides the crop of the next year, whenever the canes are in a 
healthy condition at the end of June. In the Barbadoes it 
is stated that each inch of rain corresponds to about 800 hogs- 
heads in the resulting crop, or Vqo of a hogshead of sugar to 
the acre. 

In Mauritius, it is said that the number of marriages de- 
pends on the rainfall because of its effect on the sugar crop. 
Sugar-cane should have comparatively dry weather during 
ripening and harvesting and dry weather facilitates grinding. 

526. Temperature effects on sugar-cane. — The rate of 
growth of cane increases with the temperature. Freezing 
weather kills the buds, hence the seed cane must be cut and 
windrowed in Louisiana before the temperature falls much 
below freezing. As the cane is cut in an immature state in 



244 AGRICULTURAL METEOROLOGY 

Louisiana, the longer it can continue growing the higher the 
sugar-content; hence growers formerly suffered much loss 
from fall freezes. With the present excellent warning serv- 
ice, the cane is allowed to stand until a forecast of probable 
minimum temperature of 26° to 27° is issued by the Weather 
Bureau. A large force of men is then put into the fields and 
all the seed cane is windrowed and as much of the other cane 
as practicable. After the cane is frozen, windrowing is con- 
tinued as long as it remains frozen or until only an amount 
sufficient for two weeks' grinding is left standing. The sirup 
in this standing cane which has been frozen will not spoil, un- 
less it is too warm, for about two weeks, and grinding may be 
continued. The frozen cane that is windrowed and thaws 
out slowly receives no material damage. Sometimes a warn- 
ing of damaging temperatures will result in windrowing of 
cane valued at $10,000,000 to $15,000,000. 

527. Sugar-cane in the United States. — Sugar-cane can 
be raised in all of the Gulf states, but it is not grown commer- 
cially for sugar in any quantity outside the lower Mississippi 
Delta in Louisiana. 

528. Sugar-beets. — The growing of beets for sugar is a 
comparatively recent practice, particularly in this country. 
The first factory in the United States was at Philadelphia in 
1830. In 1880 there were four factories in operation, but in 
1890 only two. In 1900 this number had increased to only 
thirty with an output of granulated sugar worth only a little 
over $5,500,000. By 1909 the number of factories in opera- 
tion was about twice that in 1900, while the granulated sugar 
output was increased nearly ten times. 

Sugar-beet factories have been built in regions where sugar- 
beets produce well, and later have had to discontinue opera- 
tions because the sugar-content was found to be too low to 
make manufacturing financially successful. 

529. Sugar-content of beets affected by temperature. — 
While the temperature and rainfall must be high enough for 
growth, it is found that moderate temperature and long hours 
of daylight are necessary to produce a high sugar-content. 
It must be cool during the ripening period especially, and 
there should be large diurnal variations in temperature. 

It is found that the successful beet districts are in regions 
where the mean temperature during the growing months is 



WEATHER AND MISCELLANEOUS CROPS 245 




246 AGRICULTURAL METEOROLOGY 

not far from 70°. Fig. 72 shows the summer isotherm of 70"^ 
while a region on each side about 100 miles in width fairly 
well outlines the region of most of the sugar factories at the 
present time. 

530. Sugar-beets as a winter crop. — Sugar-beets are suc- 
cessfully raised in southern California and parts of Arizona 
and New Mexico by making part of the growth in the winter 
months. The best fields in Colorado and Utah are at eleva- 
tions between 4000 and 5000 feet. A great amount of heat 
is not necessary when the plants are growing, neither will they 
thrive if the weather is cold and damp just after planting. 
Sugar-beets are very sensitive to frost when young, although 
they can stand rather cold weather in the fall. A hard freeze 
just as the plants are coming up is almost fatal. The crop 
should have about five months without severe freezing 
weather. 

531. Effects of rainfall on sugar-beets. — Heavy rains in 
the spring delay planting. Drought retards growth so that 
a uniform rainfall or supply of irrigation water is needed dur- 
ing the growing period. From a five-year experiment in Utah, 
it was found that when watered each week, 1 inch weekly gave 
a higher yield than any other quantity. It was determined 
in Indiana that the rainfall should be not less than 2 inches 
or over 4 inches a month. Experiments have shown that a 
heavy rainfall is followed for several days by a reduced sugar- 
content. It should be rather dry during ripening as heavy 
rains may cause continued growth and a lessening of the sugar 
values. 

532. Temperature for sugar-beets. — The limiting factors 
in successful beet-sugar production are too warm weather in 
the summer and too cold weather in winter for winter pro- 
duction. The difference between day and night temperatures 
should be large while ripening. The sugar-content will in- 
crease as the temperature decreases. In regions near the 
southern limit of the best production, a cool summer and fall 
produces the best results. 

533. Sunshine for sugar-beets. — Sugar is made by the 
action of light on the green leaves when moisture and car- 
bonic acid gas are present. Actual sunshine is not so impor- 
tant as long hours of daylight, hence the sugar-content in- 
creases with increases in latitude. 



WEATHER AND MISCELLANEOUS CROPS 247 

534. Correlation studies of sugar-beets. — The correlation 
coefficient between the average temperature for June, July, 
and August and the sugar-content of beets raised in 1901 to 
1904 at five different places in the eastern part of the United 
States was —0.53 with a probable error of =t=0.11. The corre- 
lation coefficient between the June average temperature and 
the tonnage in the United States was —0.67, probable error 
=t0.10. Curves showing the relation between the mean tem- 
perature for either June, July, or August, or these months 
combined, and the sugar yield in different states and the Uni- 
ted States, gave in practically all cases a decreased 3'ield with 
an increased temperature. 

535. Weather and maple products. — A study of the effect 
of weather on the yield of maple products covering thirteen 
years in Portage County, Ohio, showed that February should 
be warm and that March must be cool for the best results. 
The curves for the March mean or maximum temperature 
and the yield have an opposite tendency. The correlation 
coefficient between the mean temperature for March and the 
yield was —0.69, probable error ±0.08. Out of the six years 
when March was cooler than the normal, the yield was above 
the average every year but one. That year the mean was 
only slightly above normal while the yield was only 0.1 pound 
a tree less than the average. There is a chance for a very 
profitable study in this connection. 

536. Weather and honey. — There is opportunity also for 
a very interesting and valuable study of the relation between 
the weather and the yield of honey. Such studies in Iowa 
covering the period from 1885 to 1914 showed that an abun- 
dant but not excessive rainfall in Maj^ is desirable. June, 
which is the honey month, should be drier than normal for 
best yields. A rainy period is generally a time of decreased 
production. Clear days before a rain show a slightly greater 
increase than the days immediately following. 

537. Temperature and honey. — A cold March is unfavor- 
able for a good honey year. A record of the total yields of 
honey at different maximum temperatures for all single days 
recorded in 1885 to 1914, showed the following: 



248 AGRICULTURAL METEOROLOGY 

Maximum Percentage of 

temperatures honey -production 

Less than 70° 1 per cent 

70 to 800 ' 8 " " 

80 to 900 53 " " 

90 to 100 37 " " 

Over 100 1 " " 

Considering all days for the months of June, July and 
August. 



Temperatures 

All days less than 80° 
" " 80 to 90 
" " over 90 


Percentage of total 
honey produced 
17.3 
45.4 
37.3 


TOBACCO 





Tobacco was used by the natives in North, Central, and 
South America when first visited by Europeans. There are 
three general classes of tobacco grown in this country, each 
of which is best developed under specific climatic and soil con- 
ditions. 

538. In the United States. — The two most extensive dis- 
tricts of tobacco-culture in the United States are in northern 
and western Kentucky, including northwestern Tennessee, 
and southwestern Ohio, and in northern and eastern North 
Carolina and southern and central Virginia. Smaller though 
intensive areas are in southern Wisconsin, south-central 
Maryland, southeastern Pennsylvania, and north-central 
Connecticut, while a considerable amount is raised in north- 
eastern South Carolina. 

539. Climate and tobacco. — The distribution of the crop 
shows that it is extensively grown under quite wide variations 
of temperature and rainfall. The tobacco plants are very 
susceptible to frost; hence, the seed is planted in beds and the 
plants are set in the fields after all danger from frost is over. 
The beginning of transplanting varies from the latter part of 
March in northern Florida to the first part of June in Wis- 
consin and New York. The crop is generally ready to cut 
and house about three months after it is transplanted; hence, 



WEATHER AND MISCELLANEOUS CROPS 249 

there is occasionally damage from fall frosts in the northern 
states. 

540. Under shade. — Considerable tobacco is grown under 
cloth shade, particularly in the Connecticut Valley. The ef- 
fect of the covering is to conserve the moisture of the soil, 
increase the temperature and relative humidity of the air, 
and reduce the wind velocity. 

541. Weather and tobacco. — Tobacco is a weed and 
grows most rapidly with plenty of moisture and warm 
weather. In the shade experiments, it was found that the 
rate of growth increases with higher temperature and de- 
creases with lower. If there is a decided drop in temperature, 
there is a decrease in the growth which continues for a day or 
two after the temperature has begun to rise. If the plants 
get a good start after transplanting, they will stand practi- 
cally dormant during a drought and will then grow rapidly 
when rain comes. 

542. In Kentucky. — A study of the weather and yield of 
tobacco in Kentucky covering a period of twenty years 
showed that June should be warm and wet to produce the best 
yields, although there were some marked exceptions to that 
rule. Neither the mean temperature nor the total rainfall 
for July was a determining factor in varying the yield. Rain- 
fall in August was favorable, while the best yields followed a 
rather dry and cool May. 

543. In Ohio. — A comparison of the yield of tobacco in 
Ohio with the temperature and rainfall departures from the 
normal for the state as a whole from 1881 to 1907 shows little 
relation, probably from the fact that tobacco is grown only 
in parts of the southern and western portions of the state. 

544. Darke County, Ohio. — This is the most important 
tobacco-growing county in Ohio. Two independent studies 
have been made in this county covering the period from 1886 
to 1909. Both investigators found that a wet August was 
desirable and that the months of June and July combined 
should be slightly cooler than the normal. No relation was 
observed between the yield and either the mean maximum 
or mean minimum temperatures, or the number of rainy days. 

545. Montgomery County, Ohio, 1883 to 1908.— June 
should be warm, as a cool and dry month is decidedly unfavor- 
able to the yield. Hot weather kills the cutworm. Too much 



250 AGRICULTURAL METEOROLOGY 

rain in this month will force the plants into top. July should 
be cooler than normal, as the average temperature is a little 
too high unless the rainfall is above normal. If the rainfall 
is much above the average, it ijiterferes too much with culti- 
vation. August should be cool if it is dry, as hot and dry 
weather is decidedly unfavorable. Warm and wet weather 
is most favorable for growth, but is likely io develop rust. 

546. Southwestern Ohio. — This study covered the coun- 
ties of Darke, Miami, Preble, Montgomery, Warreil, and 
Butler, from 1863 to 1913, inclusive. The following correla- 
tion table does not include 1875. That year the rainfall for 
June, July, and August totaled 22.7 inches or 7.8 inches 
above the normal, while the yield of tobacco was 470 pounds 
below, showing conclusively that the rainfall was too great 
for best yield. 

Table 54. — Correlation Between Weather and Yield of Tobacco 
IN Southwestern Ohio, 1863 to 1913 

Rainfall Temyerature 

Period Correlation Probable Correlation Probable 

coefficient error coefficient error 

July +0.21 ±0.09 +0.03 ±0.10 

August +0.56 ±0.06 -0.30 ±0.09 

July and 

August... +0.43 ±0.08 -0.21 ±0.09 

While this table shows that August is evidently the most 
critical month, possibly some other period could be found 
which has a more direct control on the yield. The student 
states that '^A study of the original data indicates that the 
highest yield of tobacco is produced when the combined rain- 
fall for July and August is about 3 to 4 inches above the nor- 
mal. A greater excess is usually quite detrimental to a high 
yield. When the rainfall for August is about normal it seems 
that the July rainfall is the large controlling factor." 

547. Summary. — The conclusions drawn from the above 
are that May should be moderately dry for a good seed-bed, 
and cool to harden the tobacco plants. June should be mod- 
erately warm and wet to insure growth when the plants are 
set out, unless the warm and wot weather develops bed-rot; 
July rainfall and temperature not far from normal, as too 



WEATHER AND MISCELLANEOUS CROPS 251 

much rain interferes with cultivation; if dry, the temperature 
should be below the normal. August should have rain enough 
to produce a good sized leaf after topping. Warm and wet 
weather makes the best growth but is more likely to cause 
the development of rust. Hot and dry weather is very detri- 
mental; hence if the rainfall is less than normal the month 
should be cool. If the growing season is moderately wet with 
a uniform supply of moisture, the best growth will be with 
the temperature somewhat above normal. But if drought 
prevails or frequently occurs, the best results are obtained 
with the summer somewhat cooler than normal. 

548. Tobacco root-rot. — While this disease is influenced 
by moisture and condition of the soil, the soil temperature 
is the most important factor affecting its extent. The most 
favorable soil temperatures for the development of the dis- 
ease range from 62° to 74°. Below 59° the disease is less 
marked, while above 90° practically no infection occurs. 
June is the most favorable month for the development of to- 
bacco root-rot, from a temperature standpoint. A heavy in- 
fection in June may be overcome by a very warm July. 

SEEDS 

549. Effect of weather on maturing seed. — It has been 
found in England by Hooker that the weather during the 
maturing of peas and beans has a very great effect on the 
yield of the crop from this seed. The ripening period must be 
dry. The lack of rainfall at harvesting time, making it b}^ no 
means rare to gather and thrash a crop of seeds without its 
having been touched by a drop of water, is one of the reasons 
why beans and peas and short-season seeds raised in Idaho 
and other semi-arid states are in such demand. 

550. Seeds from drier regions. — It is commonly better 
to use seed grown in a region of smaller rainfall during matur- 
ing, particularly in a comparatively dry district. Also in- 
stead of using seed that matured during wet weather, it is 
better to discard that and obtain seed from a drier region or 
even to use seed one year older if that was grown under the 
more favorable conditions of less rainfall and more sunshine. 

551. Alfalfa seed. — The alfalfa crop that is saved for 
seed should have warm wet weather or ample storage mois- 
ture at the beginning of its growth, followed by fair and not 



252 AGRICULTURAL METEOROLOGY 

too hot weather during blooming. A mean monthly temper- 
ature somewhere in the middle seventies is evidently favor- 
able for the plant at the critical period of blooming. The 
season of growth and harvesting of seed must be quite free 
of frost. 

552. Potato seed. — Immature potatoes or at least those 
not over-ripe are best for seed. Northern-grown potato seed 
is preferred not only because it may be less ripe when har- 
vested, but is stored where it is kept dormant and solid. A 
temperature of 32° to 40° is best in storage in order to main- 
tain the dormancy of the tubers. 

553. Wheat seed. — Spring wheat seed obtained from 
farther north will ripen earlier and give a better yield and 
quality than seed from the same strain ripened farther south. 
Winter wheat seed, on the other hand, from points farther 
south will give better yields than northern-grown seed of the 
same variety. 

554. Regions especially favorable for seed. — There are 
well-recognized localities especially favorable to the produc- 
tion of seeds of high quality. For example, alfalfa seed will 
mature well only in the dry climate of the semi-arid West. 

Some of the common opinions about these matters have 
not been wholly verified, but they are so general and are so 
evidently a climatic matter that they are worth mentioning. 
Onions grown from California seed are different in keeping 
quality from those from Michigan seed; cabbage, cauliflower, 
and the like, head better from seed grown on Long Island or 
in the Puget Sound region than from any other section; to- 
mato plants raised from seed produced in northern states are 
far superior to those from seed in the South. 

555. Good " seed " weather. — It is probable that po- 
tatoes and turnips yield best when ripened in cool weather; 
that most of the cereals, clover, and most grain seeds are 
better ripened under warm conditions, while beans, peas, and 
some other legumes should be ripened under dry conditions. 

PLANT DISEASES AND INSECT DAMAGE 

There is a close relation between the weather and the dam- 
age done by plant disease and by insects. In many of these 
the kind of weather that favors the most rapid development 
of the disease or of the damaging insects is well known; in 



WEATHER AND MISCELLANEOUS CROPS 253 

others it remains to be worked out, thus making it important 
that all farmers keep a careful record of the weather factors 
when disease or insect damage is prevalent and when this 
damage is checked. 

556. Terms relative. — In the designation of ''dry" or 
"wet" weather diseases and "warm" or "cold" weather dis- 
eases, it must be remembered that the writer is speaking in 
relative terms as compared with the average condition at the 
place of record. Plant diseases are not abundant in the trop- 
ics and yet various wilt and root diseases and many leaf 
troubles spread in Louisiana during the hottest weather there. 
On the other hand, many diseases common in the North are 
troublesome in Louisiana only in " cool " weather. The onion 
mildew and the bean anthracnose are well-marked examples. 

557. Bitter-rot of apples is a common and destructive 
disease in the South but it is a botanical curiosity in New Eng- 
land. Apple-scab, on the other hand, is more prevalent in 
northern districts. Pear-blight is also a disease common only 
in warmer regions. 

558. Late blight of potatoes. — In extreme northern dis- 
tricts this is spoken of as a "warm" moist weather disease, 
while in slightly more southern states it is known as a "cool" 
moist weather disease. It develops with greatest rapidity in 
moist weather, but the optimum temperature for its most 
rapid development is at about 72'^. 

Contrasted with the potato Phytopthora is the allied dis- 
ease, cucurbits, the downy-mildew, which appears to flourish 
during hot seasons and to disappear in cool ones. In Wiscon- 
sin the summer of 1915 was cool and moist and the late blight 
caused immense damage to potatoes, but the cabbage crop 
was everywhere vigorous. In 1916 it was hot and dry and 
while there was practically no potato late bhght, cabbages 
were "swept as if by fire" by the yellow disease Fusarium 
conglutmans. 

559. Wet weather diseases. — It is agreed by all plant 
pathologists that the presence of water is necessary for the 
spread of bacterial diseases. All fungi are also favored by a 
large amount of moisture while some develop most rapidly 
under conditions cooler than normal and others are favored 
by temperatures higher than normal. An example of the last 
named condition is the "scab" or "black-spot" of cucumbers 



254 AGRICULTURAL METEOROLOGY 

which sometimes causes much damage in the pickle-growing 
regions of Michigan, Indiana, and Wisconsin. 

560. Dry weather diseases. — Some of the most well- 
defined dry weather diseases are the point-rot of tomatoes, 
the cabbage black-rot and the southern bacterial wilt of po- 
tatoes known as the '' sleeping sickness." 

561. Grain rusts. — Hot and humid weather at the ripen- 
ing period favors a rapid development of rust and these con- 
ditions in many years limit the southern development of 
successful wheat-growing. In the spring wheat region of the 
Northwest, stem-rust often does great damage; in 1904 it was 
estimated that the loss from rust in North Dakota, South Da- 
kota, and Minnesota amounted to $10,000,000. The con- 
ditions favorable for rust in that region are muggy, sultry, 
rather still, hot days with foggy cool nights at about the blos- 
soming period. Just after the infection, cool, moist, slow- 
growing, showery weather may result in widespread damage. 

562. Spread by the wind. — Bacteria being present in the 
leaf surface water film, are splashed up by the impact of fall- 
ing raindrops, and these bacteria-laden drops are carried by 
the wind to a distance proportional to its velocity. The dis- 
tance of the splash varies according to the size of the drop, 
depth of surface film, elevation and inclination of the surface 
of impact, and the velocity of the wind. Faulwetter found 
that with a wind of ten miles an hour a drop of rain 0.02 cc. 
in volume falling 16 feet the splash was carried in abundance 
8 feet, in moderate quantities 12 feet, and in slight amount 
16 feet, while a wind of thirty miles an hour carried the splash 
at least 50 feet. 

563. Smuts. — It has been found that the soil tempera- 
ture at the time of germination is an important factor in the 
development of the stinking-smut of wheat. The most favor- 
able temperature is between 59° and 72° while a soil temper- 
ature above 72° or below 41° is decidedly unfavorable for the 
development of the disease. For this reason, winter wheat 
sown very early in warm soil or very late in cold, in the Pacific 
Northwest, is comparatively free from the disease. It has 
been found that the soil temperature is an important factor 
in the development of the Fusarium wilt of potatoes, as well 
as another Fusarium disease the '^ flax-wilt." In some exper- 
iments the flax developed normally when the soil temperature 



WEATHER AND MISCELLANEOUS CROPS 255 

was held continuously below 59°, but if the temperature rose 
above 61° even for one day, infection occurred and wilt de- 
veloped. 

564. Insect damage. — It is well recognized that the ac- 
tivity of insects is affected by weather conditions, and that 
they cause more damage some seasons than others because 
of the characteristics of the weather. 

565. Grasshoppers. — It is generally experienced in the 
middle and western states that when two dry summers occur 
in succession, the second one usually has a serious outbreak 
of grasshoppers. Dry weather favors the hatching of the eggs 
while in cool wet weather the grasshoppers often die in large 
numbers from disease. 

566. Chinch-bugs. — Warm dry weather is favorable for 
an increase in chinch-bugs. A succession of dry summers, 
especially in May and the first part of June, and in August 
and the first of September, thus covering the two hatching 
periods, is very likely to cause an outbreak in a region subject 
to infection. The damage by chinch-bugs in thirt^^-eight 
counties in Illinois in 1914 was estimated at $6,400,000. The 
year was very dry, particularly in June, and there was a 
marked absence of heavy beating rains from May to August. 
This year was one of a series of rather dry summers in the 
region of infestation from 1910 to 1914. The next year the 
late spring and summer were cooler than normal and there was 
an abundance of heavy rain-storms which put an end to the 
destructive outbreak in one season. 

567. Temperature and chinch-bug. — It was found in 
Illinois that the chinch-bug does not ordinarily begin its 
movements until the temperature reaches 74°, while on hot 
bright days its activities cease from 10 or 11 o'clock until 
3 or 4 p. m. It was observed that they make little or no move- 
ment after twilight. 

568. Effect of wind on insects. — The chinch-bug tends 
to move with the wind especially when on the wing. Warm 
days, with strong winds after rain or dull days, showed a rapid 
advance to the leeward. In New England it was found that 
the gipsy moth made a general progress of five miles a year 
toward the northeast, the direction of the prevailing winds, 
while the spread was only three miles a year toward the west. 

569. Cutworms. — A study in Marion County, Ohio, 



256 AGRICULTURAL METEOROLOGY 

showed that the weather during May exerted a strong influ- 
ence on the damage done by cutworms. It was found that a 
cool and wet May was favorable to cutworm activity, while 
a warm and dry May was unfavorable. The correlation coef- 
ficient between temperature in May and the percentage of 
damage to corn in the county was —0.50, probable error 
=±=0.11. It was +0.34, probable error =b0.14, between rain- 
fall and damage. 

570. White-grub. — It was found that the correlation co- 
efficient between the temperature in May and the percentage 
of damage by the white-grub was —0.55, probable error 
=1=0.11, and between rainfall and damage +0.51 and probable 
error d= 0.11, showing that a cool and wet May was also favor- 
able to the activities of this pest. 

571. Hessian fly. — Augestine found that the highest cor- 
relation between weather and damage by the hessian fly was 
with a warm October and a dr^^ April. The correlation co- 
efficient between the October temperature and damage was 
+0.62, probable error, ±0.10, and between April rainfall 
and damage, —0.72, probable error =t0.08. 

572. Insect pests and parasites. — The effect of the 
weather on parasites or fungous diseases of insects may be 
different from that on the insects themselves. For example, 
the oat aphis breeds and multiples at a temperature of about 
40° or above, while the common parasite of this and many 
other aphids is not active at a temperature below 56°. Con- 
sequently, a mild winter and cool spring, when the tempera- 
ture fluctuates between 40° and 56°, permits the aphis to 
multiply unchecked by the attacks of the common natural 
enemy. At a temperature of about 70°, however, the para- 
site will multiply about ten times as rapidly as its host, hence 
at that time the plant-lice are soon destroyed by the parasite. 

573. Cattle-tick. — A study by Cotton and Voorhees 
showed that zero weather is fatal to the cattle-tick in all 
stages, unless the tick is on an animal or in a well-protected 
building. Adults were killed at a temperature of 14°, the 
seed ticks at 4°, and eggs at 2°, when exposed under condi- 
tions similar to grass in ordinary pastures. They found that 
the ticks will not permanently occupy a territory where zero 
temperatures occur, or where the mean relative humidity is 
below about 60 per cent. 



WEATHER AND MISCELLANEOUS CROPS 257 

LABORATORY EXERCISES 

(1) A study of the effect of the weather during the ripening of seed on 
its viability and vigor is of much importance. Whenever germination 
records are available covering any considerable number of years, corre- 
lations may be made with the weather condition. 

(2) Another problem that needs more study is the influence of differ- 
ent soil temperatures on germination; Time necessary and percentage 
of germination. 

REFERENCES 

Vegetables 

California Agricultural Experiment Station Bulletin 294. 

Colorado Experiment Station Bulletin 209. 

Cornell University Reading Course, No. 112, Vol. V, 1918. 

Effect of Weather on the Yield of Potatoes. J. Warren Smith, Monthly 
Weather Review, May, 1915. 

Home Gardening in the South, Farmers' Bulletin 934. 

Investigations of the Potato Fungus Phytopthora Infestans. L. R. 
Jones and others, Bureau of Plant Industry Bulletin No. 245. 

New York State College of Agriculture, Reading Courses, Lesson No. 
124. 

Oregon Experiment Station Bulletin No. 122. 

On the Occurrence of Phytopthora Infestans and other diseases. A. D. 
Selby, Ohio Naturalist, February, 1907. 

U. S. Department of Agriculture Bulletin, 561. 

Utah Experiment Station Bulletin No. 157. 

Potato Culture. Chas. D. Wood, New Jersey State Board of Agricul- 
ture, 36th Annual Report, 1909. 

MISCELLANEOUS 

Alfalfa Seed Growing and the Weather. J. Cecil Alter. Utah Agri- 
cultural College Experiment Station, Bulletin No. 171, 1920. 

A New Interpretation of the Relationship of Temperature and Humid- 
ity and Insect Development. W. D. Pierce, Journal of Agricultural 
Research, March 20, 1916. 

Beet-Sugar Industry in the United States, U. S. Department of Agri- 
culture Bulletin No. 721. 

Illinois Experiment Station Circular 189. 

Influence of Environment on the Chemical Composition of Plants. 
H. W. Wiley, Yearbook, 1901. 

Iowa Experiment Station Bulletin No. 169. 

Irrigation of Sugar-Beets, Farmers' Bulletin No. 392. 

Journal of American Society of Agronomy, Vol. 8, No. 5, pages 299-309. 

North Dakota Experiment Station Bulletin 68. 

Ohio Agricultural Experiment Station Circular 115. 



258 AGRICULTURAL METEOROLOGY 

Phylopathology. L. R. Jones, The Plant World, August, 1917. 

Sugar-beet in America, The. F. S. Harris, The Macmillan Co., 1919. 

Sugar-beets in Indiana, Indiana Experiment Station Bulletin No. 68, 
Vol. IX. 

Strains of White Burley Tobacco Resistant to Root-rot, U. S. Depart- 
ment of Agriculture Bulletin, No. 765. 

Tennessee Agricultural Experiment Station Bulletin No. 94. 

The Hessian Fly and how to Prevent Losses from it. W. R. Walton. 
Farmers' Bulletin 1083, March, 1920. 

Tobacco. G. N. Coffee, Monthly Weather Review, 1907, page 346. 
^ Tropical Agriculture. E. V. Wilcox, D. Appleton & Co., 1916. 

Utah Experiment Station Bulletin No. 156. 

Wind-blown Rain, a Factor in Disease Dissemination. R. C. Faul- 
wetter, Journal of Agricultural Research, September 17, 1917. 



CHAPTER X 

WEATHER FORECASTS AND WARNINGS 

The United States Weather Bureau issues regular forecasts 
of the weather twice each day, while special forecasts and 
warnings are put out whenever the conditions warrant. 

574. Forecast centers. — District centers, at which fore- 
casts are made for a district covering several states, are lo- 
cated at the Central Office in Washington, D. C, and at Chi- 
cago, Illinois, Denver, Colorado, New Orleans, Louisiana, 
and San Francisco, California. 

575. A. M. forecasts. — The morning forecasts are made 
at about 9. a. m., eastern time, and cover the probable condi- 
tions thirty-six hours in advance. These forecasts are imme- 
diately telegraphed from the centers to about 1600 principal 
distributing points, whence they are further disseminated by 
telegraph, telephone, wireless, and mail. These are the fore- 
casts that appear in the afternoon papers. 

These forecasts reach nearly 100,000 addresses by mail, 
and are available to more than 5,500,000 telephone sub- 
scribers within an hour after the time of issue. Many thou- 
sands of persons never think of starting on a trip, or of taking 
up any important work that is affected by the weather with- 
out calling up the Weather Bureau Office or the nearest tele- 
phone exchange and asking for the official forecast for the 
next thirty-six hours. 

576. Value of forecasts. — Shippers of perishable products 
must know the forecasts. Commission-men and other ship- 
pers of perishable products in most of the important cities 
always delay their morning shipments until they know from 
the forecasts what temperature to expect and how to prepare 
their goods for it during transit. The railway and transpor- 
tation companies make continuous use of the forecasts in all 
their shipments. Often shipments of perishable goods are 
accelerated or protected against temperature extremes by 
icing or heating, as conditions may require. Bananas, for ex- 

259 



260 AGRICULTURAL METEOROLOGY 

ample, must be kept at a temperature of 58° to 65° during 
shipment, as a temperature below 55° chills the fruit suffi- 
ciently to cause a deterioration in quality, while a tempera- 
ture above 65° inside the car will produce over-ripening. The 
shipment of live-stock by freight is avoided, if possible, when 
a hot wave is expected. High temperatures are hurtful to 
certain other shipments, such as fish and oysters, so that the 
question of the proper amount of ice to be used is intimately 
connected with the forecasts issued. 

577. Special forecasts for agricultural interests. — Some 
of the special forecasts issued for and widely used by the agri- 
cultural interests are the following: 

Alfalfa cutting. — Throughout the principal alfalfa-growing 
districts, special three or four day fair weather forecasts are 
issued at harvesting time. 

Sheej) shearing and lamhing. — Special forecasts of snow or 
rain, especially with wind and low temperature, are widely 
distributed in the West at shearing and lambing time so that 
shearing may be delayed or if done sheep may be protected, 
and extra precautions taken to care for young lambs. 

Spraying forecasts. — It has recently been necessary to have 
spraying experts in important apple and other fruit-growing 
districts and even to detail special weather forecasters to 
these regions so that spraying may be done before rainy pe- 
riods to prevent the rapid dissemination of apple-scab and 
other diseases. 

Raisin-drying. — In the raisin-growing districts of Califor- 
nia, rain forecasts are of great value. The raisin crop while 
drying is extremely susceptible to injury from rains, and the 
forecasts enable the growers to stack and protect the drying 
trays. Rain forecasts are also utilized in the large fruit-grow- 
ing districts to hasten picking before a rain, so that the fruit 
can be shipped while dry. 

578. P. M. forecasts. — The evening forecasts are made 
at about 9 p. m. eastern time, and cover the two following 
days. These forecasts are sent throughout each district by 
the Press Association wire service. These appear in the 
morning newspapers. 

579. Local forecasts. — The weather forecasts at district 
centers are for states or sections of states. At most of the 
other Weather Bureau Offices, the official in charge amplifies 



WEATH'ER FORECASTS AND WARNINGS 261 

or modifies these state forecasts to cover the probable condi- 
tion in the particular city or vicinity where each office is lo- 
cated. 

These forecasts are based on a knowledge of the weather 
that is prevailing throughout the country and certain well-de- 
fined laws of the weather, 

580. Observations. — A record of the pressure, tempera- 
ture, weather, wind, clouds, humidity, amount of rainfall, 
and extremes of temperature during the preceding twelve 
hours, and the like, is made by trained observers at about 200 
different points at 8 a. m. and p. m , eastern time. 

Within five minutes after these observations are made, a 
telegraphed message in code, giving all the essential weather 
facts, is filed at the local telegraph office and by an ingenious 
*' circuit" system is placed in the hands of the Weather Bu- 
reau officials at Washingtion and at about 180 other stations 
in the country, within thirty minutes after the instruments 
are read. 

581. Weather maps. — As fast as the telegrams reach the 
various offices, the data are charted by trained men on out- 
line maps of the United States, so that by the time the last 
report is received the forecaster has a complete weather map 
before him. 

When these maps are completed, each forecaster has before 
him an actual picture of the weather that prevailed through- 
out the country half an hour previously. He can see the 
pressure and temperature of the air, not only at his station, 
but at every other station. He knows where it is raining or 
snowing; the amount of precipitation that has fallen at each 
place during the preceding twelve hours, the wind direction 
and velocity, the kind, amount, and direction of move- 
ment of the clouds; where and when thunder-storms oc- 
curred and any other fact that is of importance regarding 
weather. Used in connection with a similar map of twelve, 
twenty-four, thirty-six, and forty-eight hours before, he can 
trace the movement of the various weather conditions from 
place to place. 

582. Weather laws. — A study of the daily weather maps 
shows that the wind does not "blow where it listeth," but 
that there are well-defined laws that regulate the wind and the 
movement of storms and general weather conditions. 



262 



AGRICULTURAL METEOROLOGY 



583. 1st law: weather moves eastward in temperate 
latitudes. — In the temperate latitudes in both the southern 
and northern hemispheres, the weather conditions move in a 
general easterly direction with a fair regularity of motion. 
This is the most important law of storms. The atmosphere 
near the surface of the earth moves in wave-like areas of high 
and low pressure. Fig. 73 shows the average paths over 




Fig. 73. — Average tracks of high and low pressure areas in the 
United States as they move from west to east. The broken lines 
running from northeast to southwest show the average distance 
traveled each twenty-four hours. 



which these areas move in the United States, as well as the 
average distance traveled each twenty-four hours. 

584. 2nd law : the direction of surface winds depends on 
the difference in pressure. — On the weather maps (see 
Figs. 74 and 75), the solid Ikies are those of equal barometric 
pressure or isobars. 

The word ''high" indicates the centers of the high pressure 
areas and the word ''low" centers of low pressure. Arrows 
on the maps show the wind direction at the time the obser- 
vations were made. The arrows fly with the wind, and it will 
be seen that the wind blows toward the center of the lows, 



WEATHER FORECASTS AND WARNINGS 263 

and away from the center of the highs. This is the second im- 
portant law of the weather. 

A wind from the east on the Atlantic Coast is usually fol- 
lowed by a rain because the wind is blowing toward a storm 
that is approaching from the west. These low-pressure areas 
or storms are usually accompanied by rainy weather and rain 
begins to fall when the center gets near enough. After the 
storm center passes by, the wind shifts to westerly, as it still 




Fig. 74. — 'A typical winter storm Dec. 15, 1893, that is central over 
southern Iowa. 



blows spirally toward the center, and fair weather usually 
follows. 

585. 3rd law: the temperature at any place is largely 
controlled by the wind direction. — The dotted or broken 
lines on the weather maps are lines of equal temperature or 
isotherms. It will be seen that these temperature lines curve 
to the north in front or to the east of the lows, where the 
winds are from the south, and curve toward the south to the 
west, or in the rear of the lows where the winds are from the 
north. It is warm in front of the low pressure areas because the 
winds are coming from a warmer region. North winds bring 
cooler weather because they are coming from a cooler region. 



264 AGRICULTURAL METEOROLOGY 

586. 4th law: pressure areas and weather. — Low-pres- 
sure areas are usually accompanied by cloudy weather with 
rain or snow, while high-pressure areas are more likely to be 
attended by clear skies and fair-weather. As these areas move 
eastward, they carry along with them the weather, tempera- 
ture, and wind variations described above. 

587. Weather forecasts are made for any particular 
region by estimating the path and rate of movement of a 




Fig. 75. — The same storm twenty-four hours later, Dec. 16, 1893. 
The temperature lines are shown on this chart. The arrows at 
each station show the wind direction; they fly with the wind. 

low or high pressure area west of it, the probable weather that 
it will cause, how it will affect the wind direction, and through 
the wind direction the temperature. 

588. Special warnings. — In addition to the regular twice- 
daily weather forecasts, special warnings are issued for pecul- 
iar conditions and interests. Some of the most important are 
given below. 

Storm warnings. — Warnings of high winds and hurricanes 
influence the handling of the shipping all along the coasts. 

Flood warnings. — Forecasts of the height of the water in 
the large rivers can be made very accurately, days and some- 



WEATHER FORECASTS AND WARNINGS 265 

times weeks in advance. Warnings of floods are made when- 
ever it is expected that heavy rains will cause a sharp and con- 
tinued rise in the streams. Some of the most fertile soil 
is in the river valleys and warnings of damaging waters are 
very valuable and can be obtained from the river district 
centers. 

Cold wave warnings. — These warnings are utilized by many 
interests and millions of dollars worth of damage averted by 
their receipt. 

Frost warnings are issued for truck-growers and orchardists 
in protecting crops from fros*-; damage. (See Chapter XL) 

Warnings for stockmen. — C Id wave, high wind, and heavy 
snow warnings are issued for the benefit of stock-growers over 
the Great Plains and in the West. 

Heavy snow warnings are issued for railroads and other 
transportation companies. 

LOCAL WEATHER SIGNS 

Certain local signs are valuable in anticipating the weather 
for a few hours in advance only. These relate largely to the 
relative humidity, clouds, and air pressure. 

589. Humidity. — There is usually an increase in the 
humidity of the air before a rain because the latter is usually 
preceded by warm southerly winds that are taking up mois- 
ture as they flow northerly. Warm moist air attends a fall- 
ing pressure, and under these conditions there is a feeling of 
physical and mental lassitude that is in striking contrast to 
the feeling of exhilaration that accompanies the cool, dry, 
electrically-charged westerly winds that come with a rising 
barometer. The lower animals and insects, a,s well as humans, 
are undoubtedly affected by these cond'*:ions. 

590. Good rain-indicators. — Certain phenomena are 
brought about by increasing moisture i^Ad hence are good 
rain-indicators. Some of these are : sweating walls, sidewalks, 
metal plates, and dishes; tightening of ropes; increase in per- 
fume of flowers; softening of moss; shortening of guitar 
strings; increase in odor from drains and ditches; tightening 
up of curls, and the like. The American Indians say: ''When 
the locks turn damp in the scalp house, surely it will rain." 
Floors saturated with oil become very damp, salt increases 
in weight, and tobacco becomes moist before a rain. 



266 AGRICULTURAL METEOROLOGY 

Corn fodder is very sensitive to any increase of moisture in 
the atmosphere and becomes damp and Ump before a rain. 
It is said that before a rain the leaves of many trees are turned 
up or twisted over so as to show more of the under side, and 
if this is true it is probably caused by the absorption of mois- 
ture from the atmosphere by the wood fibers in the stem. 

591. Moisture in vapor form. 

When the stars begin to huddle, 
The earth will soon become a puddle. 

''When the sky is full of stars, expect rain." When there 
is an increased amount of moisture in the atmosphere in the 
form of vapor, there is usually a greater homogeneity of the 
atmosphere, hence its transmissibility for both light and 
sound waves is increased. For this reason when the amount 
of water-vapor increases, stars that are usually visible only 
with a telescope may be seen with the naked eye. Under sim- 
ilar conditions, sound is carried more readily and the singing 
of birds and the calls of domestic fowl are plainer and more 
noticeable. This is why ''parrots whistling indicates rain," 
and 

When the peacock loudly bawls, 
Soon we'll have both rain and squalls. 

592. Pressure of the atmosphere.^ — The differences in air 
pressure are not great enough at any single point to be no- 
ticeable to man. It seems possible, however, that the differ- 
ence in the supporting power of the air between high pressure 
(usually fair weather) and low pressure (usually stormy 
weather) condition makes some difference in the flight of 
birds, and has thus led to "Everything is lovely and the goose 
hangs (honks) high," and the saying that swallows and mar- 
tins fly low just before a rain, and that bees remain in or near 
their hives just before stormy weather may be expected. 

It has often been noticed that water will begin running in 
ditches that are fed by springs just before a rain, although 
they have been quite dry. This is undoubtedly due to the 
fact that the decreased weight of the atmosphere in a low 
pressure area allows the ground water-level to rise slightly. 

593. Wind and pressure. — When the wind sets in from 
points between south and southeast and the barometer falls 
steadily, a storm is approaching from the west or northwest, 



WEATHER FORECASTS AND WARNINGS 267 

and its center will pass near or to the north of the observer 
within twelve to twenty-four hours, with winds shifting to 
the northwest by way of southwest and west. When the wind 
sets in from points between east and northeast, and the ba- 
rometer falls steadily, a storm is approaching from the south 
or southwest, and its center will pass near or to the south or 
east of the observer within twelve to twenty-four hours, with 
winds shifting to northwest by way of north. The rapidity 
of the storm's approach and its intensity will be indicated by 
the rate and the amount of the fall in the barometer. 
694. Clouds. 

If clouds look like they had been scratched by a hen, 
Get ready to reef your topsails then. 

When ye see a cloud rise out of the west, straightway 

ye say "There cometh a shower"; and so it is. — Luke XII, 5-1. 

The clouds are the "storm signals of the sky," and by 
watching them carefully very accurate prognostications can 
be made for a few hours in advance. 

595. High clouds. — The high cirrus and cirri-stratus 
clouds are particularly valuable in this respect, especially if 
they are of the thin wispy type sometimes called ''mare's 
tails." These clouds are composed of ice spicules and are 
formed by the condensation of moisture in high altitudes, 
that has been carried up in a storm area that perhaps is west 
of the observer and is moving toward him. 

596. Hales, or large circles around the sun and moon, 
are formed by the refraction of light through these ice parti- 
cles and are frequently indicative of stormy weather. If the 
high clouds are moving rapidly eastward and the sky below 
is partly covered with denser clouds moving westward, then 
the storm is approaching rapidly and will probably cause 
heavy rain and strong wind. 

597. Low clouds. — Lower clouds are so closely connected 
with the rainfall that they are generally of little value in in- 
dicating the weather for any considerable time in advance. 
When the lower clouds begin to break up and enough clear 
sky can be seen 'Ho patch a Dutchman's breeches," fair 
weather may be expected very soon. 

598. Fog or mist. — "When Lookout Mountain has its 



268 AGRICULTURAL METEOROLOGY 

cap on, it will rain in six hours." This is true in general with 
other mountains, but only "when the fog goes up the moun- 
tain you may go hunting, but when it comes down the moun- 
tain you may go fishing." 

LONG-RANGE FORECASTS 

Weather forecasts of a quite general nature are made for a 
week in advance by the Weather Bureau, by enlarging the 
observational field through daily reports by wireless and cable 
from different places in the northern heinisi^here. 

599. Seasonal forecast not yet possible. — It is not pos- 
sible at the present time, however, to predict storms for a 
longer time than a week or ten days in advance, and the gen- 
eral weather of a month or season in advance cannot 3'et be 
determined. The officials of the Weather Bureau believe that 
the time will come when seasonal forecasts can be made, but 
it cannot be done at the present time with sufficient accuracy 
to warrant the attempt. Some of the most able scientific men 
of the century are at work on the problem, and sufficient has 
become known to be sure that it nnist be solved through a 
stud}' of the solar energy alone and its effect on the atmos- 
phere. 

600. Planets have no known effect on the weather. — The 
planets have no effect whatever on the weather, and the effect 
of the moon is so slight as to be outside of consideration. No 
forecasts that pretend to predict the movements of storms 
for weeks in advance should be taken seriously, and all efforts 
to make predictions of the weather for months in advance, 
based on the movements of the planets, appear to be utterly 
unreliable. 

601. Animals, birds, and plants. — In connection with the 
long-range forecasts, it may not be out of place to state also 
that animals, birds, and plants show by their condition the 
character of past weather and by their actions the influence 
of present weather, and possibly the character of weather 
changes that may occur within a few hours, but never the 
weather that may be expected during the coming winter or 
sunnner. Also that the weather of certain days, months, 
seasons, or years, affords no reliable indications of future 
weather, but show present abnormal conditions that the fu- 
ture may adjust. 



WEATHER FORECASTS AXD WARNINGS 2f39 

LABOKATOKY EXERCISES 

1. Paragraph 08 1. Practice should be given in making daily weather 
maps. The necessary data can he obtaincnl from the publishe^l tables 
or from the nearfist Weather Bureau Office, 

2. Paragraph 582. A series of weather maps covering successive 
four to six day periods can be obtained from the Weather Bureau and 
from their use in the class the varioas "weather" laws can be demon- 
strated, and from them forecasts can be attempte<^l. 

The student will soon see that forecasting the weather is not so easy 
as it first seems and that there are marked exceptions to general rules. 

3. Paragraphs o89 Uj 508. Forecasts should be regularly made from 
local weather .signs. This will .soon show that it cannot be done for 
any considerable time in advance. 

REFERENCES 

Weather Forecasting in the Unite^I States. U. S. Weather Bureau, 1916. 



CHAPTER XI 

FROST AND THE PROTECTION OF CROPS 
FROM FROST DAMAGE 

The limiting factor in the successful cultivation of many 
crops is the usual date of the last killing frost in spring and 
the first frost in autumn; and in themselves, frosts are likely 




Fig. 76. — Average dates of last killing frost in the spring. 

to set the bounds for much of the farm work. The relation 
of frost to crop-production may now be considered. 

602. Average killing frost dates. — The average dates of 
the last killing frost in the spring and the first in the fall are 
shown respectively by Figs. 76 and 77 for the different sec- 
tions of the country. Frost may be expected one year in two, 
on an average, on the dates indicated, while the dates when 
frost may be expected only one year in ten will be about two 
weeks later in the spring and two weeks earlier in the fall. 

270 



FROST AND FROST DAMAGE 



271 



603. The growing season. — The potential growing season 
in any locality is usually considered to be the average number 
of days between the spring and fall killing frost dates. A 
map showing these days is given in Fig. 78. 

For tender crops that are killed by frost, the possible grow- 
ing season is less than indicated on the chart, because the 
killing frost dates are for the average when frost occurs one 
year in two. Killing frosts occur after the spring and before 
the fall date frequently enough to make the possible length 




Fig. 77. — Average dates of the first killing frost in the fall. 

of the growing or frost-free period frequently less than the 
average. 

Further, such crops as are not killed by temperatures at or 
somewhat below freezing, have a longer possible growing sea- 
son than the frost-free dates. Winter grains and grass, for 
example, will continue to grow in the fall after a killing frost 
and will begin growing in the spring and winter long before 
the average spring killing frost date, if favorable tempera- 
tures prevail. 

604. Vegetative periods. — The temperature at which 
most field and garden crops will begin to grow is probably 
close to 6° (C.) or 42.8° F. Hence the growing or ''vegeta- 



272 



AGRICULTURAL METEOROLOGY 



tive" period for the crops that are not killed by ordinary 
frosts may be considered as that between the date in the 
spring when the average daily temperature rises to 43°, and 
the date in the fall when the mean daily temperature falls to 
43°. 

605. Comparison of the vegetative with the frostless 
period. — The vegetative or potential growing period is 
longer than the frostless period in all parts of the United 




Fig. 78. — Average number of days between killing frosts. 

States, except over a small area along the north Pacific Coast, 
as shown by Fig. 79. This difference varies from less than 
twenty days in a few places in the northern part of the 
country to over 100 days in the northern part of the Gulf 
states. 

606. The true growing season. — The normal growing 
season, therefore, should be the average vegetative period 
and not the frost-free period, for the reasons given above. 

607. Extending the growing period. — In those regions 
where the vegetative period usually begins a month or more 
before the last killing spring frost, and extends as long a time 
after the first fall frost, it has been profitable to protect ten- 
der crops from frost damage by artificial means, and thus 



FROST AND FROST DAMAGE 



273 




274 



AGRICULTURAL METEOROLOGY 



make their possible growth period agree more nearly with 
that of the hardy crops. 

The protection of fruit and truck crops from frost is en- 
tirely practicable but whether economically profitable de- 
pends on the value of the crop saved and the expense of pro- 
tection. 

608. When frosts occur. — Areas of high barometric pres- 
sure spread across the United States from the west toward the 




Fig. 80. — Daily weather map showing an area of high pressure with 
a cool wave in the Northwest that may be expected to over- 
spread Ohio in the next forty-eight hours with general frosts. The 
solid lines are drawn for equal barometer pressure while the dotted 
lines are drawn through places with equal temperature. The 
arrows fly with the wind and show wind direction. 

east at an average rate of 400 to 600 miles in twenty-four 
hours. They are usually preceded by strong northwesterly 
winds which cause a drop in temperature ; if it is in the winter 
and the fall in temperature is rapid and extreme it is termed 
a "cold wave," while in the summer the phenomenon is 
spoken of as a "cool wave." 

After the windy front of the high pressure area or "anti- 
cyclone" has passed by and the center of the high overspreads 
a district, it generally causes clear and comparatively quiet 



FROST AND FROST DAMAGE 



275 



air. The air is so clean and clear that it may seem very warm 
in the sunshine, but continues keen and cool in the shade. At 
night the surface of the ground and objects upon it cool rap- 
idly by radiation and in turn cool the lower layer of air by 
conduction, and, if it is in the spring or autumn, the temper- 
ature of the plants and of the air in contact with them may 
fall to the freezing point and frosts occur. Figs. 80, 81, and 
82 show the movement of an area of high pressure across the 




Fig. 81.— The high pressure area shown in Fig. 80 is spreading 
southeastward and is causing general frosts in Ohio. Light, 
heavy, and kilUng frosts are shown by appropriate words. 

Lakes and the Ohio Valley that was accompanied by general 
and widespread frosts. 

609. Local conditions favorable for frost.— The local con- 
ditions which indicate the central portion of an area of high 
pressure are clear and nearly still air with the temperature 
falling quite rapidly in the afternoon and early evening; with 
clear skies because the radiation of heat from the ground and 
plants is most rapid in clear weather; with nearly still air be- 
cause under these conditions the air arranges itself in layers 
with the colder heavier air at the surface of the ground, es- 
pecially in low places. This line of temperature variation is 



276 



AaUICVLTURAL MI'JTmHOLOGY 



so well inarkod sonuM iiuos (h;it the iVuil on the lower part of 
a two will 1)(' killed by frost whiles i\\r. upper piirt will escape 
dainnji;e nnd l)(\'ir ;i <>;()()d v.vup. 

610. Principles of frost protection. — To prevent damages 
from frost, action must be taken to coiuiteract, so far as pos- 




M^y P, /9/4 



Fio. S2. — The same area twenty-four hours later. It overspreads 
Oiiio and frosts are widespread. The temperature will rise 
gradually as the area moves eastward. 

sil)l(^ the conditions favorable for frost. Hcnco the following 
l)recauti()ns should be (a,k(>n: 

(1) Dinunish tlu^ radiation of heat at night by covering 
with wood, })apei-, or cloth, or by building snmdge fires that 
surroiuid the trees or plants with artificial clouds of smoke. 

(2) Locate orchards and early gardc^n crops on the hillsides 
and not in low places, so that the air which has been cooled 
by conduction to the surface of the ground will slide slowly 
away into tlu^ valley and be replaced by th(^ warmer horizon- 
tally moving air wliich ovcm'Hc^s the coldcu- air in the valleys 
when conditions of inversion prevail. 

(3) By mixing the air so as to })i'(^v(nit its forming in 
lay(^rs. 

(4) Adding lu^at to tlu^ air. Tt has been demonstrated that 





Plate VIII. — (Upper) The California short-stack oil heaters in place 
in an orange grove. (Lower) Improved tall-stack down-draft oil 
heaters burning at night. The lower portions of the stack are red 
hot and there is verv little smoke. 



FROST AND FROST DAMAGE 



277 



by building a large number of small fires in the orchard or 
throughout the truck fields not only will heat be added, but 
the lower part of the atmosphere will be kept in circulation 
so that laj^ers of cold air will not form. 

611. Protection from frost damage by building fires. — 
The adding of dry heat to the air, thus warming up the cold 
lower layer and mixing the cold lower layer with the warmer 




Fig. 83. — Lard-pail type of oil heater, and one of the first invented, 

layer immediately above has come to be the best accepted 
method for frost protection. 

612. Kinds of fuel. — Fires may be made of oil, coal, 
wood, or any other material that will burn readily. The fuel 
to be used in any particular orchard will depend on its rela- 
tive accessibility and the labor available. 

613. Oil-heaters. — There are some ten to fifteen different 
types of oil-heaters on the market, varying from 1 to 6 gallons 
in capacity and costing from 20 cents to several dollars each. 
(Fig. 83 and Plates V to VIII.) The oil-heaters should be 
set at the rate of 80 to 120 to an acre. The temperature 
must be watched closely and when it has fallen nearly to the 



278 AGRICULTURAL METEOROLOGY 

danger point, every third or fourth heater should be Hghted 
and then the others as needed. The fires should be thicker 
on the outside edge, especially on the windward side, and also 
in low places. 

614. Oil consumed. — The round heaters of the lard-pail 
type with the top about 7 inches in diameter will burn at a 
rate of about one quart an hour. With fifty pots of the one- 
gallon capacity burning to the acre, twelve and one-half gal- 
lons of oil will be consumed an hour for each acre. With 
heaters constructed so that the burning surface can be con- 
trolled, the intensity of the fires can be varied as the temper- 
ature conditions demand. 

The number of hours that the heaters will be burned will 
vary with the season, crop, and location. If one stores 400 
gallons of oil for each acre, it will allow for burning 100 one- 
gallon pots to the acre for twelve hours, which is sufficient 
for most seasons in the deciduous orchards. It is usually nec- 
essary to provide for longer burning periods and a much 
longer critical period in the citrus orchards. 

615. Kind of oil. — The most desirable oil for fuel is a 
refinery product of about 20 to 26 degrees Baume. Crude oil 
is used considerably, but it is likely to contain a small amount 
of water, and when such does exist the oil is liable to boil over 
after a short time, just when the fire is needed most. Oil with 
a parafine base burns much cleaner than that with an asphal- 
tum base. Light gravity oil burns too readily, while too 
heavy oil does not burn clean and a large amount of soot is 
deposited on the trees. 

616. Lighting heaters. — Special or home-made torches 
may be used in lighting the heaters. The time necessary de- 
pends on the type of heaters, kind of torches, the number of 
heaters lighted to the acre, and so on. Under very favorable 
conditions, one man can light over 500 fires in an hour, while 
100 an hour would be a good number where the pots are scat- 
tered or do not light quickly. 

617. Cost of equipment. — The initial investment for 
equipping a ten-acre orchard for oil-heating, including tank, 
cistern, heaters, and the like, under average conditions will 
not be far from $500, or $50 an acre. After the first year, the 
cost of heating including labor and fuel will approximate $3 
to $5 an acre for each night. 



FROST AND FROST DAMAGE 



279 



618. Coal-heaters (see Fig. 84) cost more than the 
cheaper oil-heaters, but only about half as many are set to 
the acre. The best coal-burners hold 25 to 30 pounds of coal 
and will burn from four to six hours. It is considered that 
one ton of coal equals 100 gallons of oil in heating value. At 
one Ohio orchard in 1914, the temperature was kept 9 degrees 
higher within the orchard than was recorded outside the 





^^^^^^IPIggJII^g 








7^4'^--.^T 'C5*;^..;C "■■■'^^''''*| 



Fig. 84. — A type of coal heater that will hold about 18 pounds of 
soft coal. They will burn seven or eight hours. 

heated area with thirty-six coal fires to the acre. Oil-soaked 
waste and kindlings are placed in the bottom of the coal- 
heaters before they are filled. They are then lighted with a 
torch fully as fast as the oil-heaters. Coal is often placed in 
piles about the orchard, thus saving the cost of heaters. It 
must be remembered that a few large piles of coal to the acre 
will not furnish adequate protection, but that the more small 
piles the better. 

619. Wood fires. — Fires have been made of old rails, brush, 
and cord wood. In using cord wood, the sticks are piled with 
the ends dove-tailed together and as these ends burn off the 
sticks are pushed together. About six sticks of hardwood 



280 



AGRICULTURAL METEOROLOGY 



will burn four or five hours. Wood needs more attention than 
either coal or oil and the fires must be started earlier. (See 
Fig. 85.) 

620. Great care needed. — Experience has shown that 
one must go about orchard-heating in a throughly business- 
like manner. There must be plenty of fuel, men enough to 
keep the fires going and to make preparation for the next 




Fig. 85. — Wood piled for orchard heating. 

night's fight, and constant vigilance until the frost season is 
over. Care must be taken not to waste the fuel by lighting 
the fires too early or on nights when not needed. 

621. Critical temperature. — Thermometers should be dis- 
tributed throughout the orchard and watched closely, and 
when the temperature approaches the danger point the light- 
ing should be begun in the lowest part of the orchard. If the 
temperature is falling slowly, the fires need not be started 
until the temperature is very close to the danger point. This 
is especially true with oil-heaters as the effect of the burning 
oil is almost immediately noticed; it takes longer for the coal 
and wood to get started. If the temperature is falling rapidly, 



FROST AND FROST DAMAGE 



281 



however, and the conditions seem to favor a low record, the 
fires must be lighted while the temperature is still several de- 
grees above the danger point. (See Table 11 for data show- 
ing the critical point for many of the fruits.) Tender truck 
crops need to be protected from freezing temperatures also. 
622. The lowest temperature just before sunrise. — 
Fig. 86 shows a thermograph record from May 11 to 18, 1914. 
It was quite warm on the 11th, the curve indicating a temper- 
ature of 80°. A cool wave reached the region of the station 
before noon of the 12th and there was a sharp drop in tem- 
perature. There was little variation on the 13th, but from 
the 14th to 17th typical radiation conditions prevailed. The 
temperature rose to between 60° and 70° during the daytime 




Fig. 86. — Record made by a self-recording thermometer May 11 to 
18, 1914, at Delaware, Ohio. 

under bright sunshine, but fell nearly or quite to freezing at 
night with free radiation. It is under conditions like those 
of the 14th to 17th that frosts are likely to occur and, as 
shown by the record, the lowest temperature will be reached 
just before sunrise. 

623. Protection by heating possible. — Experience has 
conclusively proven that the temperature can be kept above 
the danger point by orchard-heating when otherwise it would 
fall low enough to cause damage to fruit and truck. 

Arrangements can be made to receive frost warnings by 
writing the nearest Weather Bureau Office if an effort is made 
to protect fruit or truck from frost damage. 



LABORATORY EXERCISES 



1. Paragraph 603. Obtain daily mean temperature and killing frost 
data from the local Weather Bureau and compare the frostless and 
vegetative periods. 



282 AGRICULTURAL METEOROLOGY 

2. Paragraph 605. If the vegetative period is considerably longer 
than the frost-free period, what local crops might profitably be pro- 
tected from early or late frosts? 

3. Paragraphs 610 to 619. Carry out some tests of frost protection, 
particularly to truck or small-fruit Crops, by covering or heating. 

4. Paragraph 621. The influence of topography on night tempera- 
ture should be ascertained by exposing thermometer at different ele- 
vations. 

REFERENCES 

A Study of the Effect of Freezes on Citrus in California. H. J. Webber 
and others, California Experiment Station Bulletin No. 304. 

Avoidance and Prevention of Frosts in the Fruit Belts of Nevada. 
Church and Ferguson, Nevada Agricultural Experiment Station 
Bulletin No. 79. 

Freezing of Fruit Buds, The. F. L. West and N. E. Edlefsen, Utah 
Agricultural College Experiment Station Bulletin No. 151. 

Forecasting Frost in the North Pacific States. E. A. Beals, U. S. De- 
partment of Agriculture Bulletin No. 41. 

Frost and the Growing Season. Atlas of American Agriculture, Office of 
Farm Management. 

Frost and the Prevention of Damage by It. Floyd D. Young. Farmers' 
Bulletin, 1096, April, 1920. 

Frost and Temperature Conditions in the Cranberry Marshes of Wis- 
consin. Henry J. Cox, Weather Bureau Bulletin T., 1910. 

Frost Data of the United States. P. C. Day, Bulletin V of the Weather 
Bureau, Department of Agriculture. 

Frost in the United States. Wm. Gardner Reed, Proceedings of the 
Second Pan American Congress, 1916. 

Frosts in New York. W. M. Wilson, Cornell University, Agricultural 
Experiment Station Bulletin No. 316. 

Hardiness of Fruit Buds and Flowers to Frost. Garcia and Rigney, 
New Mexico Agricultural Experiment Station Bulletin No. 89. 

KiUing of Plant Tissue by Low Temperature. W. H. Chandler, Mis- 
souri Agricultural Experiment Station Research Bulletin No. 8. 

Papers on Frost and Frost Protection in the United States. Monthly 
Weather Review, October, 1914. 

Protection from Damage by Frost. W. G. Reed, Geographical Review, 
Vol. I, 1916, No. 2. 

Studies in the Formation of Frost. D. A. Seeley, Monthly Weather 
Review, August, 1918. 

Relation of Weather to the Setting of Fruit, The. Hedrick, New York 
Agricultural Experiment Station Bulletin No. 299. 

Variation in Minimum Temperatures due to the Topography of a 
Mountain Valley in Its Relation to Fruit Growing, Batchelor and 
West, Utah Agricultural Experiment Station Bulletin No. 141. 



CHAPTER XII 
VALUE OF LIGHTNING-RODS 

There was a time when lightning-rods were a fad and the 
Hghtning-rod agent flourished and waxed fat. But because 
he insisted on accumulating the good things of the land too 
rapidly there soon came a second period when shot-guns were 
kept loaded and standing beside the outside door because the 
lightning-rod agent became more to be feared than the light- 
ning. 

But the lightning-rod that had been put up stayed up and 
it began to be noticed that those which had been installed in 
an honest and workmanlike manner furnished protection, 
while all around buildings without such protection were being 
destroyed by lightning. This has led fire-protection agencies, 
appalled by the immense fire loss, to inquire more fully into 
the possible value of lightning-rods as a protection. 

624. Thunder-storms. — All the features of thunder- 
storms point to their dependence on a convectional overturn- 
ing of the atmosphere. Thunder-storms usually occur wher- 
ever there is a rapidly rising current of moisture-laden air. 
Condensation goes on rapidly in such a rising mass of air as 
soon as the dew-point temperature is reached and at such 
times electricity accumulates very rapidly. As clouds form, 
different clouds or parts of the same cloud may be charged 
with various kinds of electricity, negative or positive. Great 
changes in electrical potential are caused which may result 
in lightning. 

625. Where thunder-storms occur. — Thunder-storms oc- 
cur most frequently in warm regions and are commonest in 
spells of warm summer weather and in the afternoon shortly 
after the warmest part of the day. 

In the United States the greatest number occur in the east 
Gulf states where the average days with thunder-showers 
each year will be close to sixty. In Missouri and eastern Kan- 
sas it will average over fifty, while in the whole central valley 
country from the Appalachian to the Rocky Mountains and 

283 



284 AGRICULTURAL METEOROLOGY 

from South Dakota and southern Minnesota and Wisconsin 
to the Gulf the average number each year is over thirty. 

In New England, upper Michigan, and practically all of 
the region in and west of the. Rocky Mountains, except in 
New Mexico and Arizona, the average annual number of 
thunder-storm days is less than twenty. In the Pacific Coast 
states they are very rare. 

626. Nature of lightning. — Lightning is an electric spark 
on a tremendous scale. It occurs between clouds more fre- 
quently than between cloud and earth. The length of the 
flash between the cloud and the earth is usually not more than 
one mile in length, while within clouds it may be twenty miles 
in length. Lightning flashes usually consist of a number of 
successive discharges which follow each other with a very 
short interval between. In one case of a flash consisting of 
five successive discharges, the total time from the first to the 
last was found to be 0.2447 second, while the intervals be- 
tween the successive discharges were found to be 0.0360, 
0.0364, 0.0283, and 0.1440 second, respectively. One photo- 
graph showed forty distinct discharges in a single flash. 

627. Damage by lightning. — Damage by lightning is 
mechanical as well as thermal. Not only is the damage 
caused by main discharges, but currents are induced in nearby 
metal objects and conductors and these often produce ad- 
ditional damage. It is probable that most of the unusual re- 
sults in a lightning flash are due to these induction effects. 
This will be shown by a fire being started in inflammable ma- 
terial between two nearly parallel wires or rods. 

One example reported is of a fire in a flour-mill where it 
was evident a fire started on a separator between the fan- 
shaft and the drive shaft bearings. In this case the mill had 
a metal roof and was iron-clad, a protection that is considered 
to be absolute as far as any damage to the exterior of the 
building is concerned. This same writer believes that these 
induction effects between the wires on baled hay are respon- 
sible for many otherwise unexplainable fires in properly pro- 
tected barns or warehouses. 

Another writer, secretary of a company carrying risks in 
farm propert}^ of fully $42,000,000, states that all of the losses 
and damages by lightning which they have had on rodded 
buildings have iDeen traced to some metal parts, which were 



VALUE OF LIGHTNING-RODS 285 

not connected to the lightning-rod. They find that the tele- 
phone line in houses is the most dangerous thing with which 
they have to contend. He states that they find lightning will 
jump ten, twelve, arid fifteen feet from the lightning-rod to 
the telephone wire and the same from the telephone line to 
the hghtning-rod. They now advocate placing the ground 
rod on the house as near as possible to the telephone wire 
without touching it. 

628. Loss by lightning greatest in rural districts. — The 
property loss by lightning in the entire country averages ap- 
proximately $8,000,000 each year, the greater part of which 
occurs in rural districts. In the central part of the country, 
the loss and damage by lightning is far greater in the country 
than in the cities. The Indiana Fire Marshal states that 75 
per cent of all lightning losses occur in the rural districts 
which contain but 47 per cent of the population. He states 
further that in 1913, 92 per cent of all barns damaged by light- 
ning were in the country and that 69 per cent of all barn losses 
were total. In the case of dwellings, 52 per cent damaged or 
burned by lightning were in the country and 48 per cent in 
the city. 

It is stated on good authority that about four times as 
many barns are fired by lightning as houses. 

629. Office of the lightning-rod. — There is a nearly con- 
stant interchange between the electricity in the earth and 
that in the atmosphere and one of the offices of the lightning- 
rod is to furnish a path for the quiet discharge or interchange 
of this electric current. The second office of the rod is to fur- 
nish a path for the disruptive discharge between the clouds 
and the earth when the potential reaches the breaking point. 

630. Value of lightning-rods. — In 1914 the author sent 
letters of inquiry to over 1100 Mutual Fire Insurance Com- 
panies doing business in forty-four different states mostly in 
the rural districts. They were requested to report in detail 
the actual records from their books. 

Replies from 130 different companies doing business in fif- 
teen states showed that they had kept their records in such 
detail that full information could be given. These companies 
had about 350,000 farm buildings insured, valued at close to 
$300,000,000. These reports were tabulated and are sum- 
marized in the table following. 



286 



AGRICULTURAL METEOROLOGY 



o 

I ^ 



i- 



y^ Ox y^ \-L 
^,^ CO O 

O ?S CO to 



CO h-' 
J-* O to CO 
O) ^^fi. O) J-' 

C^ CO O O 
Oi -vj Cn CO 



Number of insurance com- 
panies reporting 

Number of farm buildings in- 
sured 



<:^ i^'ll ^tx Nufnber of buildings burned 
^^ o^ I^ § Z'"^'^* "^2/ cause 



O M 

CO Ci 



Number of buildings struck by 
lightning 



^ g o 00 Number struck, only damaged 



h-. t^ l_a 

-J Oi Oi Oi 

-^ Or lO (4^ 



^ to 4i^ lO 

o h-' 00 t4^ 



to H- 

C5 W o 00 

^ ~o "oo "co 

^ to 00 H+^ 
J-'J^:) CO CO 

S 2 o o 
o o o o 
o o o o 

m 

jr' I-' oi CO 

CJ 00 -4 Ci 

.50 Oi to JO 

CO '^5 00 ~0 
to Oi rfi. o 
O CO rfi. CO 

rfi- ^ S CO 

00 ;j ^j-4 

to ^rf^ Or g 
Cn 4^ 00 g 



^ to to 



M Oi s 
Cn CO CO ^ 

Cn hfi' H- r^ 



Number struck and burned 

Number struck that had light- 
ning-rods 
Number with lightning-rods 
struck and damaged 

Number with lightning-rods 
struck and burned 



Total risks on farm buildings 



Total claims paid from all fire 
loss on farm buildings 



Total claims paid due to 
lightning 

Total claims paid due to light- 
ning on rodded buildings 

Percentage of buildings rodded 



I 



o 

> 

o 

o 

tr" 

*-Q q 
> *j^ 

^§ 
"■^ 

a 



VALUE OF LIGHTNING-RODS 287 

631. Lightning-rods as a protection to buildings. — This 
table shows that the total number of buildings struck by 
lightning in 1912 and 1913 was 1845. Inquiry developed the 
fact that close to 31 per cent of all of the buildings insured by 
these companies are equipped with lightning-rods. Hence, 
if rodded buildings were just as likely to be struck by light- 
ning as unrodded ones, there would be 31 per cent of the 1845 
buildings that were struck by lightning that would have rods 
on them. As a matter of fact, however, only sixty-seven of 
the buildings struck had rods of any kind. The number of 
rodded buildings that were struck, therefore, was only 10 per 
cent of the expected number, demonstrating the fact that 
the efficacy of the lightning-rod in actually preventing dam- 
aging lightning strokes is 90 per cent. 

In a report covering the past five years, fifty-one different 
companies having nearly 95,000 buildings insured, had 660 
buildings struck by lightning, only twenty-one of which had 
lightning-rods on them. As fully 34 per cent of their build- 
ings are rodded, the expectation would be that 34 per cent 
of 660 or 224 would be rodded. But as only twenty-one were 
rodded instead of 224, or only 9 per cent, it shows that one 
may expect that out of every 100 farm buildings struck by 
lightning nine of them will be equipped with lightning-rods 
and ninety-one will not have rods. A table made up from 
sixty-seven different companies in Missouri, Illinois, and Ohio 
showed practically the same efficiency. 

Five companies doing business in Illinois, Missouri, and 
Nebraska with over 18,000 buildings insured, made reports 
covering a longer period of years, the shortest being thirteen 
years and the longest twenty-five years. They have had no 
building burned or even materially damaged by lightning 
that was equipped with rods, and they report over 50 per cent 
of their buildings rodded. T'his is an efficiency of 100 per 
cent. 

This finding of the efficacy of the lightning-rod in prevent- 
ing damaging lightning strokes is substantiated by the results 
of an inquiry by W. H. Day of the Ontario Agricultural Col- 
lege. His inquiry covered Ontario, Iowa, and Michigan and 
included several years. He found the efficacy of the light- 
ning-rod m preventing lightning strokes to be from 92 to 99.9 
per cent. 



288 AGRICULTURAL METEOROLOGY 

632. Damage to rodded buildings. — Occasionally a 
rodded building is struck by lightning, but the properly in- 
stalled lightning-rod is of very great value in preventing dam- 
age. , ^ 

The table shows that the total claims paid on farm build- 
ings due to lightning, in 1912 and 1913, was $336,171. Inas- 
much as 31 per cent of these buildings insured by these com- 
panies were rodded, a loss would be expected on rodded 
buildings of 31 per cent of $336,171 or $104,213, but in fact 
the total claims paid for lightning damage on rodded build- 
ings during the two years was only $13,053. In other words, 
the actual loss was only 12 per cent of what would have oc- 
curred if the lightning-rods did not serve as a protection. 

The total number of buildings burned by lightning in 1912 
and 1913 as reported by these companies was 407, and of 
these only nine were equipped with lightning-rods, or only 2 
per cent. Of those struck that had rods, only 5 per cent were 
burned and the other 95 per cent simply damaged : thus show- 
ing that the danger of a building being burned by lightning 
that is equipped with lightning-rods is exceedingly slight. 

A further study of the reports shows that when struck and 
damaged by lightning but not burned down, the average dam- 
age to a building was less than $10 on those equipped with 
rods and very nearly $200 when not so equipped. 

633. Material for lightning-rods. — Lightning-rods may be 
of iron, copper, or aluminum and either will be satisfactory 
as a conductor. As iron is not so good a conductor as copper, 
it is thought to carry a lightning flash more safely, and be- 
sides it has the advantage of having a higher fusing point. 
Iron rods must be heavily galvanized and kept painted fre- 
quently and for this reason should not be used in locations 
difficult of access. 

If single-strand iron rods are used, they should be No. 2, 
No. 3, or No. 4 (B. and S. gage) depending on the size of the 
building; No. 2 is 0.257 inch in diameter or about twice the 
size of an ordinary telegraph wire which is No. 9; No. 3 is 
0.244 inch and No. 4 is 0.225 inch in diameter. Star section 
rods are preferred by man}^ 

The Michigan Agricultural Experiment Station recom- 
mends the use of 3/8-inch seven-strand iron cable as being 
easy to handle, inexpensive, and wholly satisfactory. The 



VALUE OF LIGHTNING-RODS 289 

important thing seems to be to have it heavily galvanized and 
kept painted. , • -j 

634. Copper rods.— The best type of a copper rod is said 
to consist of bundles of small wires twisted tightly together. 
A steady electric current flows through every part of a con- 
ductor, but when the current is variable and exceedingly 
rapid the flow may be confined to a film very near the surface. 
To carry a lightning discharge, therefore, the rod should have 
as large a surface as possible. A twisted rod with thirty 
wires each 0.0425 inch in diameter has about five and one- 
half times the surface of a round solid rod with the same 
amount of material. 

The National Board of Fire Underwriters recommends that 
on residences, barns, stables, stores, and similar buildings 
where the maximum height of any point does not exceed 60 
feet, copper cable be used, weighing not less than 3 ounces a 
foot and no single wire being less than 0.046 inch m diameter. 
In the case of taller and larger buildings, they recommend 
the cable to weigh not less than 6 ounces a foot. 

635. A continuous conductor necessary.— The all-impor- 
tant thing seems to be to have a continuous conductor from 
the highest points on the building to permanently moist 
earth beneath. The kind of material and the size of the rod 
does not seem to be so important as frequent inspection, good 
groundings, and constant care to see that there are no poor 
or broken joints or rusted and broken connections. 

636. Points above all projections. — Points should extend 
above all chimneys or other roof projections and should be 
placed at each gable end and at intervals of 25 to 30 feet along 
the ridge. There should be two grounds to all rod systems 
and if the buildings are 100 feet or more in length, three or 
more down rods. All cables should be connected in one s^^s- 
tem. Insulators should not be used but the rod fastened di- 
rectly to the sides of the building. All heavy masses of metal 
in the building should be connected to the rod, but the rods 
should be kept as far away as possible from gas-pipes or lead 
water-pipes. . 

637. Grounding the rods.— The earth connection may be 
a square sheet of copper 1/16 inch in thickness and not less 
than 3 feet square. This must be buried in moist earth even 
if one has to go down 10 or 12 feet. Probably the most eco- 



290 



AGRICULTURAL METEOROLOGY 



nomical and at the same time satisfactory grounding is made 
with cast iron or copper rods extending into the earth from 
6 to 10 or more feet, or to a point well below the foundation 
walls of the building to be protected. 

Farmers' Bulletin 842 illustrates satisfactory methods for 
grounding wires, connecting exterior and interior metal work, 



■^ 



Fig. 87. — Lightning-rod on a small general barn, 

erection of roof points, and the like, in a very complete man- 
ner. (Figs. 87, 88.) 

638. How spliced. — When splices are necessary, the ends 
must be fastened solidly together and if possible riveted and 
soldered. When there is an imperfect connection, the elec- 
trical resistance will be so great that the electricity is likely 
to leave the rod and damage the building. Metal-covered 
roofs should be connected with ground wires from at least 
two corners by riveting and soldering and then run to moist 
earth. 



VALUE OF LIGHTNING-RODS 



291 



639. Care in installing. — While lightning-rods must be 
put up in a workmanlike manner, their installation involves 
no more wonderful or mysterious processes than building a 
fence or digging a well. 

The statement by some lightning-rod agents that no one 
but special scientists versed in all of the laws of electricity 
should do the work of putting up lightning conductors is 




Fig. 88. — Method of placing points and connecting rods on a farm- 
house to protect from hghtning. 

about as sensible as to say that no one but a professor of ge- 
ometry should be allowed to lay brick. And not only that 
but any professional in the lightning-rod business who advo- 
cates that his system is the only one scientifically correct and 
reliable, while all others are worthless and dangerous, invites 
the suspicion that he is himself a fakir. 

The installation of a proper rod is not and need not be ex- 
cessively expensive. By the exercise of ordinary common 
sense and with the knowledge that electricity demands a con- 
tinuous path to the moist earth, a satisfactory rod can be put 
up without serious trouble. 



292 AGRICULTURAL METEOROLOGY 

640. Loss of live-stock. — The loss of live-stock near wire 
fences is very great. It may be reduced by grounding wire 
fences by means of galvanized iron pipes or posts at intervals 
of about 100 yards or by attaching wires to the posts at about 
the same distances and letting them extend well into the 
ground. Care must be taken to see that these ground wires 
are in contact with each fence wire, and that they go into 
moist ground. The electrical continuity of the fence should 
be broken at intervals also by inserting sections of non-con- 
ducting wood in place of the fence wire. 

LABORATORY EXERCISES 

1. Paragraph 630. An inquiry of the local Mutual Fire Insurance 
Companies regarding losses on rodded and unrodded buildings would 
give some valuable data. 

2. Paragraph 637. Copies of Farmers' Bulletin 842 should be ob- 
tained for detailed instruction in instalhng lightning-rods. 

3. Paragraph 640. An inquiry of local stock-growers would develop 
some interesting and valuable data regarding loss of stock near un- 
grounded wire fences. 

REFERENCES 

EfRciencj' of Rods in Preventing Lightning Damage, The. W. H. Day, 
Ontario Agricultural College Bulletin 220. 

Lightning and Lightning Conductors. J. Warren Smith, Annual Report 
Mutual Fire Insurance Association, 1915. 

Modern Methods of Protection against Lightning. R. N. Covert, 
Farmers' Bulletin S42. 

Protection of Life and Property against Lightning, Bureau of Stand- 
ards, Technologic Paper No. 56. 



INDEX 



The numbers refer to the page 



Absolute humidity, 9. 
Agricultural climatology, 28. 

meteorology, 23. 
Agriculture, 63. 
Alfalfa, 92, 239-241, 251, 252. 

seed and frost, 240, 241. 

water requirements, 92. 
Aliquot, 77, 78. 
Almonds, 125, 126, 139. 
American Indian and corn, 149. 
Anticyclone (high pressure area), 

262-264, 274. 
Aphis, 256. 

Apples, 96, 126-129, 139, 253, 260. 
Apricots, 129, 130, 139. 
Asparagus, 219. 
Atmosphere, 1, 2, 4, 8, 15, 226. 

composition, 1, 2. 

circulation, 15. 

how cooled, 4. 

how warmed, 4. 
Avocado (alligator pears), 130. 

Bacteria of the soil, 79, 84. 
Barley, 64, 91, 93, 142, 143. 

critical period, 143. 

temperature limits, 64. 

water requirements, 91, 93. 
Barometer, 3. 
Beans, 96, 97, 217. 

in California, 97, 217. 
Beets, 92, 96, 217. 
Bioclimatic law, 29. 

an aid in farm management, 30. 
Bitter-rot, 253. 
Boll-woovil, 122, 123. 
Broom-corn, 181. 
Buckwheat, 91, 93, 143, 144. 

water requirements, 91, 93. 

Cabbage, 217. 
Cantaloupes, 215. 
Carbon-dioxide, 1, 76, 95. 



Carbon dioxide, liberation from 
plants by daylight, 95. 

by temperature, 76. 
Carnations, 67. 
Carrots, 217. 
Cassava, 215. 
Castor beans, 215. 
Cattle-tick, 256. 
Cauliflower, 217, 218. 
Celery, 218. 
Chard, 218. 
Cherries, 130, 139. 

critical temperature, 139. 
Chinch-bugs, 255, 256. 
Chinooks, 19, 97. 
Citrus fruits, 136-139. 

lemons, 96, 137, 139. 

hmes, 137. 

oranges, 136, 137, 139. 

pomelos (grape-fruit), 138. 
Climate, 

and crops, 61. 

and farm operations, 101. 

and man, 28. 

and number of crops, 103. 

continental, 61, 62. 

depends on, 61. 

important factors: 
moisture, 93. 
sunshine, 93. 
temperature, 64. 
wind, 97. 

limited by temperature, 63. 

main factors in, 64. 

marine, 61, 62. 

mathematical, 61. 

mountain, 61, 62. 

natural, 61. 

physical, 61. 

solar, 61. 

three classes, 61. 

zones, 63. 



293 



294 



INDEX 



Climatic limits of crops, 

barley, 142. 

buckwheat, 143. 

clover, 241. 

corn, 144-146. 

cotton, 101, 108. 

cowpeas, 243. 

flax, 123, 124. 

fruit, 126, 129-131, 133.. 

millet, 242. 

oats, 64. 

potatoes, 222, 223. 

rice, 179 

rye, 180, 181. 

sugar-beets, 245, 246. 

sugar-cane, 243. 

timothy, 242. 

tobacco, 248. 

vegetables, 215-221. 

wheat, 63, 64, 101, 181, 183. 
Climatic zones, 63. 
Clouds, 11. 

local weather signs, 267. 

versus sunshine, 93. 
Clover, 241, 242. 
Coal-heaters, 279. 
Collards, 218. 
Condensation, 11, 283. 
Conduction, 4. 
Continental climate, 61, 62. 
Convection, 4, 5. 
Cool-season crops, 106, 215. 

barley, 142. 

buckwheat, 143. 

potatoes, 222, 223. 

vegetables, 216-219. 
Copper lightning rods, 289. 
Corn, 

an American crop, 145. 

belt, 101. 

climatic factors, 144-147. 

correlation coefficients, 158-160, 
164-168. 

four great corn States, 153-155. 

frost, 170, 171. 

germination and temperature, 149. 

injury to seed corn, 171. 

in south temperate zone, 172, 173. 

pollination and drought, 171. 

rainfall, 37, 38, 40, 41, 54, 144- 
146, 150-170. 



Corn — Continued 

critical period, 151, 153, 158- 
166. 
near blossoming, 165. 
for short periods, 158-160, 164, 

165. 
in July, 151-157. 
most effective, 166-168. 
the most important factor, 
151. 
rainfall and temperature com- 
bined, 155-157. 
raised by American Indians, 149. 
rate of growth of seedling shoots, 

69-71, 149. 
rate of seeding, 172. 
sunshine-hour, degree, 94. 
temperature limits, 64. 
thermal and rainfall constants 

and yield, 161, 164, 165. 
transpiration from, 85, 150. 
relating to drought, 172. 
two seasons compared, 169, 170. 
water requirements, 90, 91, 93, 

150, 151. 
weather during different periods 

of growth, 160-166. 
when planted, 146, 147. 
best dates for, 150. 
in relation to frosts, 147. 
in relation to temperature, 147. 
where grown, 144, 145. 
yield in Ohio, 54, 56. 

affected by July rain, 57, 155- 
158. 
zero of vital temperature, 68. 
Correlation, 34. 
coefficient, 53. 
curve fitting, 41, 46. 
dot chart, 37. 
least squares, 41, 46, 47. 
normal equations, 46, 49. 
partial or net, 5S. 
proper method, 36. 
star point method, 47, 48. 
usual method, 34. 
when mathematical correlation 
should be made, 41. 
Correlation coefficient, 
definition of, 53. 
how calculated, 54. 



INDEX 



295 



Correlation coefRcient — Continued 
in showing relation between 
weather and crop yield, 53. 
probable error, 57. 
symbol used for (r), 57. 
theory of, 53. 
value of, 57. 
weather and 

apples, 126, 128. 

barley, 143. 

clover, 241, 242. 

corn, 158-160, 164-168. 

cut-worms, 256. 

hay, 238, 239. 

hessian fly, 256. 

maple products, 247. 

oats, 175, 178. 

potatoes, 224, 227, 228, 231- 

233. 
rye, 180. 
sugar-beets, 247. 
tobacco, 250. 

wheat, 196, 197, 199, 200, 202, 
208, 211. 
Cost of oil heating, 278. 
Cotton, 

belt, 101. ' 

climatic limits, 101, 108. 

temperature principal factor, 

108, 109. 

effect on maturity, 111. 
dates of planting and harvesting, 

109, 110. 

effect of two different seasons, 

120-122. 
general weather effects, 1 1 5. 
seasonal weather, 116, 117. 
ginning and temperature, 111, 

112. 
insect pests, 122, 123. 
rainfall influence, 111-121. 
in July and August, 117-119. 
in winter, 118, 120. 
sunshine. 111. 
temperature, 108-121. 
water requirements, 92, 93. 
weather-cotton equation, 113-115. 
where grown in the United States, 

108, 109. 
zero of vital temperature, 68. 
Cowpeas, 243. 



Cranberries, 130, 131. 

critical temperature, 139. 
Critical periods of growth, 24. 

barley, 143. 

corn, 151, 153, 158-166. 

for definite climatic districts, 106. 

fruit, 138-140, 280, 281. 

hemp, 125. 

potatoes, 228-233. 

wheat, 191. 
Crop zones, 101, 102. 
Cucumbers, 215. 
Currants, 130. 
Curve fitting, 41, 45-47, 49. 
Cutworms, 249, 255, 256. 
Cyclone (low pressure area), 262- 
264. 

Dates, 67, 131. 

Dates of seeding and temperature, 68. 
corn, 147. 
oats, 68. 
potatoes, 222. 
Daylight, 
effect of, 95. 

on rate of liberation of carbon 

dioxide, 95. 
on sugar content of beets, 96. 
pigments, 95. 
hours at different latitudes, 94, 95. 
Dew, 14. 
Dew-point, 10, 283. 

depression of the, 10, 42, 43. 
in connection with predicting 
mininmm temperatures, 47. 
Diseases of crops as affected by 
weather, 
apples, 128, 129, 253, 260. 
cucurbits, 253. 
flax-wilt, 254. 
grapes, 132. 
peaches, 134. 
potatoes, 233-236. 

late blight, 234, 236, 253. 
spread bj'' wind, 254. 
strawberries, 136. 
smuts, 254, 255. 
tobacco, 250, 251. 
weather terms relative, 253. 
wheat, 185. 

rust, 185, 191, 254. 



296 



INDEX 



Dot charts, 36, 37, 40. 
Drought, 

defined, 84. 

pollination of corn, 171. 

transpiration of corn, 172. 
Dry farming, 104. 

Effective temperatures, 67, 68. 

three summation processes, 68-73. 
Eggplants, 215. 
Equations, 41, 46, 47, 49, 51. 

partial correlation, 58. 

weather-cotton, 113. 
Evaporation, 5, 9. 

amoimt of, 85-87. 

compared with transpiration, 85. 

determines efficiency of rainfall, 
87. 

from the soil, 88. 

important factor in dry rcgif)ns, 
85. 
Exponential system, 68, 69, 72, 74. 

Farm operations, 

and climate, 101. 

bioclimatic law, 30. 

butter and cheese making in Wis- 
consin, 102, 1C3. 

change in, 102. 

climate and number of crops, 103. 

distribution of rain, 103. 

dry-farming, 104. 

length of growing season impor- 
tant, 103. 

woatlier risk, 104. 
Fiber crops, 

cotton, 108-123. (See cotton.) 

flax, 123-125. (See flax.) 

hemp, 125. (See hemp.) 
Figs, 131. 
Flax, 

fiber versus seed, 124. 

in North Dakota, 124, 125. 

relation to weather, 123, 124. 

water requirements of, 92, 93. 

where grown in North America, 
124. 

wilt, 254, 255. 
Fog, 97, 217, 267, 268. 
Forage crops, 

alfalfa, 239-241. 



Forage crops — Continued 
clover, 241, 242. 
cowpeas, 243. 
hay, 102, 236-239. 
millet, 242. 
rape, 242. 
sorgo, 242. 
timothy, 242. 

weather and yield, 236-243. 
Forecasting the weather. (See 

weather forecasts.) 
Frost, 

alfalfa seed, 240, 241. 

average killing dates, 270, 271. 

conditions for, 274-276. 

corn, 170, 171. 

critical temperatures for fruit, 

138-140, 280, 281. 
flax, 124. 

fruit, 126, 131, 133, 134, 140. 
growing season, 271, 272. 
hemp, 125. 

killing of plant tissue, 140. 
limits growing season of cotton, 

109. 
most damaging when fruit is wet, 

140. 
not expected in cloudy weather, 5. 
oats, 178. 

protection from, 276. 
by fires, 277. 

coal heaters, 279. 
oil h'eaters, 277, 278. 
wood fires, 279, 280. 
risk of in farm operations, 104. 
spring dates agree with corn 

planting, 147. 
vegetative periods, 271-273. 
with temperature inversion, 5. 
Fruit, 125-141. 

critical temperatures, 138, 139, 

141. 
leaf buds versus fruit buds, 127, 

128. 
sunshine, 96. 

Germination and temperature, 

buckwheat, 144. 

corn, 149. 

oats, 68. 
Gherkins, 216. 



INDEX 



297 



Glaze, 14. 
Gooseberries, 130. 
Grains, 

water requirements of, 89-93. 

weather and yield, 14.'. 

winter killing, 208, 209. 
Grain sorghums, 181. 
Grapes, 131-133. 

critical temperatures, 132, 139. 
Grasshoppers, 255. 
Growing season, 

barley, 142. 

buckwheat, 143. 

corn, 145-149. 

cotton, 109. (See cotton.) 

flax, 124, 125. 

hemp, 125. 

in relation to frost, 271, 272. 

oats, 175. 

vegetables, 215, 216. 

Hail, 14. 

shooting hailstorms, 15. 
Halos, 267. 
Harvesting dates, 

corn, 148. 

cotton, 110. 

flax, 125. 

oats, 173, 174. 

strawberries, 135. 

wheat, 185-190. 
Hay and forage crops, 

alfalfa, 239-241. 

belt, 101, 102, 236. 

clover, 241, 242. 

cowpeas, 243. 

millet, 242. 

rainfall and yield, 238, 239. 

rape, 243. 

sorgo, 242. 

timothy, 242. 

water reqmrements, 237, 238. 

weather and jdeld, 236-243. 
Hemp, 125. 

Height of the atmosphere, 2. 
Hessian fly, 186, 189, 211, 256. 
Honey, 247, 248. 
Hops, 219. 
Humidity, 9. 
absolute, 9. 

varies with the temperature, 9. 



Humidity — Continued 

local weather signs, 265, 266. 
relative, 10. 

use in predicting minimum 

temperatures, 47. 
varies inversely with the tem- 
perature, 10. 
Hurricanes, 17, 18. 
Hygrometric equations, 51. 
Hyperbola, 53. 

Insect pests, 

cattle-tick, 256. 

chinch-bugs, 255. 

codling moth, 129. 

cotton, 122, 123. 

boll weevil and weather, 122, 

123. 
red spider, 122. 

cutworms, 249, 255, 256. 

grasshoppers, 255. 

hessian fly, 186, 189, 211, 
256. 

oat aphis, 256. 

parasites, 256. 

white grub, 256. 
Insolation, 4, 5. 
Installing lightning rods, 289- 

291. 
Instruments, meteorological, 

anemometer, 19. 

barograph, 3. 

mercurial barometer, 3. 

psychrometer, 10. 

rain gage, 7, 12, 13. 

records valuable, 31. 

thermometers, 7. 

thermometer shelter, 7. 

thermograph, 8. 
Iron lightning rods, 288. 
Irrigation, 

in humid regions, 93. 

potatoes, 224. 

sugar-beets, 246. 

rice, 180. 

wheat, 191. 

Kafir, 181. 

Kale, 218. 

KilHng frost dates, 270, 271. 

Kohlrabi, 218. 



298 



INDEX 



Laws of the weather, 261, 262. 
Least squares, 41, 46, 47. 

calculation of straight line equa- 
tion, 41, 45, 46. 
Lemons, 137, 139. 

effect of sunshine, 96. 
Lettuce, 218. 
Light, or sunshine, 

important meteorological factor, 
93. 
Lightning, 283, 284. 
damage by, 284. 

loss greatest in rural districts, 

285. 
loss of live stock, 292. 
to rodded buildings, 288. 
rods, 283. 

continuous conductor neces- 
sary, 289. 
grounding, 289, 290. 
installation, 291. 
material for, 288, 289. 
office of, 283. 
points, 289. 
splicing, 290. 
value of, 285-287. 
Limes, 137. 
Lissner's law, 77. 

Lissner's Aliquot, 77, 78. 
Local weather signs, 265-267. 

Maple sugar and sirup, 247. 
Marine climate, 61, 62. 
Mathematical correlation, 41. 
Mathematical equations, 61. 
Melons, 

effect of sunshine, 96. 
Meteorology, 1. 
Minimum temperature predictions, 

41, 47, 48. 
Millet, 89, 93, 242. 
Milo, 181. 

Moisture (see Rain), 
in the atmosphere, 28. 
condensation of, 11. 
depends upon the temperature, 

9. 
essential to life, 8. 
measuring the amount, 10. 
in the soil, 84. 
value of, 80. 



Moon, 268. 

Mountain climate, 61, 62. 
Muskmelons, 216. 
Mustard, 218. 

Native vegetation a key to field 
crops, 29. 

Natural vegetation and farm oper- 
ations, 30. 

Nitrogen, 1. 

Normal equations, 46, 49. 

Oats, 

critical period, 177, 178. 

harvesting, 175. 

rainfall, 175-179. 

range in United States, 173, 174. 

seeding, 173, 175. 
temperature at, 173. 

temperature, 175-179. 

temperature limits, 64. 

water requirements, 91, 92. 

winter, 175. 

zero of vital temperature, 68. 
Oil heaters, 277, 278. 

oil consumed, 278. 

torches for lighting, 278. 
Okra, 216. 
Olives, 133. 
Onions, 218. 

Optimum temperature for growth of 
maize seedlings, 70-72, 149. 
Oranges, 136, 137, 139. 

effect of sunshine, 96. 
Oxygen, 1. 

Parabola, 46. 

calculation of, 49. 

equation for, 47. 

practical application of, 52. 

in predicting minimum tempera- 
tures, 50, 51. 

must fit the data, 52. 
Parsley, 218. 
Parsnips, 218. 
Partial correlation, 58. 
Pasture belt, 102. 
Peaches, 133, 134. 

critical temperatures, 133, 134, 
139, 140. 

temperature and trees, 134. 



INDEX 



299 



Peanuts, 216. 
Pears, 134, 139. 
Peas, 218. 

effect of sunshine, 96. 
Peppers, 216. 

Phenological records, 31, 162, 229. 
Physical cUmate, 61. 
Physiological summation indices, 

68-72, 75. 
Phytopthora infestans (late blight of 
potatoes), 234-236. 
affected by moisture, 234. 
affected by temperature, 234-236. 
Planets, 268. 
Plants and weather, 
aliquot, 77, 78. 
bioclimatic law, 29. 
conditions for growth, 23. 

result of complex factors, 106. 
critical periods, 24. 

how determined, 24, 25. 
value of, 25. 
development depends on a con- 
stant aliquot, 77, 78. 
factors must be in right propor- 
tion, 23. 
growth a function of weather and 

other factors, 107. 
importance of temperature, 29, 64. 
liberation of carbon dioxide, 76, 

95. 
light, 95. 
moisture-temperature efficiency 

index, 72, 73. 
optimum conditions, 78. 
periods of growth and tempera- 
ture, 64. 
periods of rest, 64, 65. 
rainfall, 84. 

requirements vary, 23. 
seasonal development, 29. 
sunshine, 95. 

temperature and distribution, 64. 
water requirements, 88. 
Planting dates, 
corn, 146, 147. 
cotton, 109. 
flax, 124, 125. 
hemp, 125. 
oats, 173, 174. 
potatoes, 222. 



Planting dates — Continued 
tobacco, 248. 
vegetables, 219, 220. 
wheat, 185, 186, 188, 190. 

to escape hessian fly, 186, 189. 
Plant temperature, 74. 
affected by sunshine, 95. 
as affected by pigments in plants, 

76. 
as compared with air tempera- 
tures, 74, 75. 
difficulty of comparing, 76. 
fluctuations rapid, 77. 
Plums, 134, 135, 139. 

rate of blossoming, 77, 78. 
Polar belt, 63. 
Pollen, 

effect of sunshine, 96. 
Pollination, 
corn, 171. 
clover, 243. 
Pomelos (grapefruit), 138. 
Potatoes, 

critical period of growth, 228-233. 

near blossoming, 231. 
diseases, 233-236. 

late blight, 234, 236. 
harvesting dates, 223. 
planting dates, 222. 

relation to temperature, 222. 
range in the United States, 221, 

222. 
relation of weather to yield, 34- 

36, 224-228. 
seed, 252. 

temperature and yield, 40, 223, 
225. 
cool favorable, 40, 223, 225- 
228, 231-233. 
temperature, limits of, 64. 
temperature requirements, 222, 

223. 
thermal constants, 230, 231. 
water requirements of, 92, 223, 
224. 
Precipitation, 
dew, 14. 
frost, 14. 
glaze, 14. 
hail, 14. 
rain, 11, 12, 14. (See also rain.) 



300 



INDEX 



Precipitation — Continued 
sleet, 13. 
snow, 13. 
Pressure varies with altitude, 2. 
Probable error, 57. 
Proso, 

water requirements of, 89, 93. 
Protection from frost, 276. (See 
frost.) 
by fire, 277. 
coal, 279. 
oil, 277. 
wood, 279, 280. 
Prunes, 135, 139. 
Psychrometer, 10. 
Pumpkins, 216. 

Radiation, 4, 5, 275, 276, 281. 

from the soil, 79. 
Radishes, 218. 
Rainfall, 

cause of, 11. 

determines the productiveness of 
a region, 80. 

how measured, 12. 

increases with altitude on wind- 
ward side of mountain, 12. 

intensity of as affecting crops, 
14. 

in the United States, 81-83. 

percentage during the growing 
season, 82, 83. 

rain making, 14. 

tabulation, 12. 

value of, 80. 
Rain in relation to, 

alfalfa, 239, 240. 

almonds, 126. 

amount per acre, 82. 

and temperature combined, 155- 
157. 

apples, 126-128. 

apple diseases, 128, 129. 

apricots, 129. 

barley, 143. 

boll weevil, 122, 123. 

buckwheat, 143, 144. 

clover, 241, 242. 

codling moth, 129. 

cotton. 111. (Soe cotton.) 

corn, 37, 144. (See corn.) 



Rain in relation to — Continued 

correlation with yield, 158. (See 
correlation coefficients.) 

dates, 131. 

drought, 84. 

efficiency affected by evaporation, 
87. 

farm management, 103, 104. 

flax, 124. (See flax.) 

grain sorghums, 181. 

grapes, 132. 

hay, 238, 239. 

hemp, 125. 

honey, 247. 

insect damage, 255, 256. 

millet, 242. 

most important factor, 151. 

oats, 175. (See oats.) 

olives, 133. 

oranges, 137. 

peaches, 133, 134. 

plant diseases, 253, 254. 

plant growth, 84. 

potatoes, 223. (See potatoes.) 

rice, 179, 180. 

rye, 180, 181. 

seeds, 251, 252. 

strawberries, 135. 

sugar-beets, 244, 246, 247. 

sugar-cane, 243, 244. 

timothy, 242. 

tobacco, 249-251. 

vegetables, 215-219. 

wheat, 183. (See wheat.) 

yield of corn, 37, 38, 40, 41, 54. 
(See corn.) 
Raisins, 131, 260. 
Rape, 243. 
Relative humidity, 10. 

use in predicting minimum tem- 
peratures, 47, 49. 

varies inversely to the tempera- 
ture, 10. 
Remainder process, 68, 69, 72, 73. 
Rhubarb, 219. 
Rice, 

temperature limits of, 64, 179. 

water requirements of, 92, 93, 179, 
180. 

where grown, 179. 
Root rot of tobacco, 251. 



INDEX 



301 



Rose, American Beauty, 

affected by sunshine, 97. 
Rye, 180, 181. 

water requirements of, 92, 93. 

Salsify, 219. 

Saturation, 10. 

Seedling shoots of maize, 69-71, 149. 

Seeds, 251, 252. 

alfalfa, 240-242, 251, 252. 

effect of weather on, 
beans, 251. 
peas, 218, 251. 

from dry regions best, 251. 

germination of, 
buckwheat, 144. 
corn, 149. 

onion, 252. 

potato, 252. 

wheat, 252. 
Seeding corn, rate of, 172. 
Semi-arid regions, farming in, 93. 
Sheep shearing and lambing, 260. 
Shooting hailstorms, 15. 
Simultaneous equations, 46. 
Sleet, 13. 
Smuts, 254, 255. 
Snow, 13. 

and wheat, 202, 203. 
Soil moisture, 84. 

affects activity of soil bacteria, 84. 

affects plant growth, 84. 

direct source of water supply of 
plants, 84. 

evaporation, rate of, 88. 

makes food available for plants, 
84. 
Soil temperatures, 78. 

affected by sunshine, 95. 

annual ranges, 80. 

as affected by soil cover, 80. 
snow cover, 80. 

desirability of temperature rec- 
ords, 80. 

diurnal changes in, 79. 

lag proportional to depth, 79. 

effect on tobacco root-rot, 251. 

flax-wilt, 2.54, 255. 

grain smut, 254. 

loss of heat, 79. 

most favorable temperature, 79. 



Soil temperatures — Continued 

snow-cover, 80. 

source of heat, 79. 
Solar climate, 61. 
Solar energy, 94. 
Sorghums, 181. 

water requirements of, 89, 90, 93. 
Sorgo, 243. 
Soybeans, 219. 
Spinach, 219. 
Spraying forecasts, 260. 
Spring wheat, 

belt, 102, 184. 

growing period, 191. 

in the United States, 183, 184. 
as affected by temperature, 183. 
as affected by moisture, 183. 

rain, 192-199. 

seed, 252. 

seeding and harvesting, 185-187. 

temperature, 194, 190, 199. 

zero of vital temperature, 68. 
Squashes, 216. 
Strawberries, 135, 136. 

adaptation to climate, 135. 

critical temperatures, 139. 

effect of sunshine, 96. 

when harvested, 135. 
Sugar-beets, 244-247. 

sugar content affected by tem- 
perature, 244-246. 
Sugar-cane, 243, 244. 

water requirements of, 243. 
Sugar products, 243-248. 

honey, 247, 248. 

maple sugar and sirup, 247. 

sugar-beets, 244-247. 

sugar-cane, 243, 244. 
Sun scald, 96, 133, 134, 234. 
Summation processes, 68 73. 
Sunshine, 

alfalfa, 240. 

apples, 96. 

beans on California coast, 96, 97, 
217. 

corn, 173. 

cotton. 111. (See cotton.) 

effect on plants, 95. 

effect on temperature of plants, 
74, 75, 95. 

grapes, 132. 



302 



INDEX 



Sunshine — Continued 
-hour degree, 94. 

variation with latitude, 94. 
important meteorological factor, 

93, 94. 
intensity of, varies with latitude, 

94. 
sometimes unfavorable, 95, 96. 
sugar-beets, 246. 
vegetables, 215, 216, 219. 
Sweet potatoes, 216. 

Temperate belts, 63. 
Temperate zones, 63. 
Temperature, 

adiabatic change in, 6. 

annual range, 6. 

greatest over land, 6, 61. 

at which growth begins, 67. 

cold waves, 16, 274. 

diurnal range, 5. 

greatest over land, 5, 61. 
slight in cloudy weather, 5. 

effective temperatures, 67. 

for growth, maximum, optimum, 
minimum, 70. 

highest in early afternoon, 5, 281. 

inversion of, 4, 276. 

limits agriculture, 63. 

limits crop areas, 64. 

lowest just before sunrise, 5, 281. 

maximum and minimum, 8, 281. 

most important in climate, 64. 

of climatic zones, 63. 

plants, 74-77, 95. 

soil, 78. (See soil temperatures.) 

sun the source of heat, 4. 

three summation processes, 68, 69. 

vertical gradient, 7. 

warm waves, 18. 
Temperature, in relation to, 

alfalfa, 239, 240. 

almonds, 126, 139. 

apples, 126, 139. 

apricots, 129, 139. 

barley, 64, 142. 

bitter-rot of apples, 128, 129. 

blooming of timothy, 242. 

boll weevil, 122, 123. 

buckwheat, 143, 144. 
germination of, 144. 



Temperature, in relation to — Cont. 
cattle-tick, 256. 
cherries, 139. 
chinch-bugs, 255. 
clover, 241, 242. 
codling moth, 129. 
corn, 145. (See corn.) 
cotton, 109. (See cotton.) 
cranberries, 130, 139. 
critical for fruit, 138-140. 
cutworms, 255. 
dates, 131. 
flax, 124. (See flax.) 
germination, 

buckwheat, 144. 

corn, 149. 

spring wheat, 194, 196, 199. 
ginning cotton. 111, 112. 
grain sorghums, 181. 
grapes, 131, 132, 139. 
grasshoppers, 255. 
hay, 238, 239. 
hemp, 125. 
hessian fly, 256. 
honey, 247, 248. 
insect damage, 255, 256. 

parasites of, 256. 
liberation of carbon dioxide, 76. 
maple products, 247. 
millet, 242. 

oats, 64, 173, 175. (See oats.) 
olives, 133. 
oranges, 137, 139. 
peaches, 134, 139, 140. 
plant diseases, 233, 236, 253, 255. 
plant distribution, 64. 
planting dates, 67, 68, 147, 173, 222. 
pollination of fruit, 140. 
potatoes, 222. (See potatoes.) 
rice, 179. 
rye, 180, 181. 
seeds, 251, 252. 
strawberries, 135, 139. 
sugar-beets, 244-247. 
sugar-cane, 243, 244. 
timothy, 242. 
tobacco, 248-251. 
vegetables, 215-219. 
vegetation, 4, 8, 64. 
wheat, 183. (See wheat.) 
white-grub, 256. 



INDEX 



303 



Thermal belts, 62. 

Thermal constants, 67-69, 161, 162, 

164, 165. 
Thermometers, 7. 
Thunder-storms, 283. 

nature of lightning, 284. 
Timothy, 242. 
Tobacco, 248-251. 
bed-rot, 250. 

in the United States, 248. 
root-rot, 251. 
under shade, 249. 
Tomatoes, 96, 97, 216. 
Torches, 278. 
Tornadoes, 16, 17. 

shooting tornadoes, 15. 
tornado tubes, 17. 
where they occur, 17. 
Torrid zone, 63. 

Total effective temperatures, 68. 
summation process, 68. 
Lissner's law, 77. 
plant development depends on 
a constant aliquot, 77, 
78. 
plant temperature should be 

considered, 74. 
solution possible, 77. 
three methods, 68-72. 
varies with other conditions, 78. 
value of, 77. 
weakness of, 73. 
Transpiration, 

and drought, 172. 
compared with evaporation, 85. 
defined, 85. 

from corn, 85, 150, 172. 
influenced by weather, 85. 
maximum, 85. 
promoted by sunshine, 96. 
Tropical belt, 63. 
Turnips, 219. 

Unknown coefficients, 46, 50. 

van't Hoff law, 69, 7'?. 
Vegetables, 215-221. 

planting dates, 219, 220. 
Vegetation (native) a key to farm 

operations and field crops, 

28-30. 



Vegetative periods, 271-273. 

Velvet beans, 219. 

Verdant zones, 62. 

Vital temperature, zero of, 67, 68. 

Warm-season crops, 106, 107, 215, 

216. 
Warnings, special, 
cold wave, 265. 
flood, 264, 265. 
frost, 265. 
snow, 265. 
stock, 265. 
storm, 264. 
Water content of soils, 85. 
Water requirements of plants, 88, 
89-93, 150, 151, 237, 
238. 
amounts for different plants, 89- 
93, 183. 
Watermelons, 216. 
Waterspouts, 16. 
Water-vapor, 2, 8, 9, 10, 266. 
Weather, defined, 1. 
Weather and crops, 106. 

factors must be in proper propor- 
tion, 23. 
Weather and seed, 252. 
Weather-cotton equation, 113-115. 
Weather forecasts, 259. 
frost, 270, 274, 275. 
laws, 261, 262. 
local, 260, 261. 
local weather signs, 265-267. 
long-range, 268. 
observations for, 261. 
pressure variations principal fac- 
tor, 264. 
shippers of perishable products, 

259, 260. 
special, 260. 

alfalfa cutting, 240, 260. 
alfalfa seed, 240. 
raisin-drying, 260. 
sheep shearing and lambing, 

26C. 
spraying, 260. 
special warnings, 264, 265. 
weather maps, 261. 
Weather maps, 261, 274, 275. 
Weather risk, 104. 



304 



INDEX 



Wheat, 181-212. 

Australia, in, 211, 212. 

belt, 101, 181, 182. 

critical period, 191, 212. 

composition of, 185. 

distribution and rainfall, 183. 

England, in, 212, 213. 

fruiting period, 188. 

growth period, 186, 188, 191. 

harvesting, 185-189. 

hessian fly, 186, 189, 211. 

Italy, in, 212. 

northern limit, 63, ISl. 

rainfall, and, 191-212. 

rust, 185, 211. 

seeding, 185, 186, 189. 
soil temperatures, 183. 
to escape hessian fly, 186, 189. 

United States, in the, 182-184. 
White-grub, 256. 
Wilting coefficient, 

defined, 85. 

varies in different soils, 85. 
Wind, 15. 

an important climatic factor, 97. 

bacteria, 254. 

beneficial or damaging, 97, 98. 

blizzards, 18. 

chinooks, 19. 

cold waves, 16. 

depends upon the pressure, 262, 
266, 267. 

doldrums, 15. 

estimating the velocity, 20. 

flax, 124. 

Foehn, 19. 

hot winds, 19. 

how measured, 19. 

insect damage, 255. 

land and sea breezes, 16. 



Wind — Continued 

monsoon winds, 16. 

mountain and valley winds, 16. 

pressure exerted by, 20. 

spread of boll weevil, 123. 

surface currents, 15. 
interruption of, 15. 

trade winds, 15. 

tornadoes, 16, 17. 

warm waves, 18. 

what makes it blow, 15. 
Winter wheat, 

belt, 101, 182. 

growing period, 188, 191. 

hessian fly, 186, 189, 211. 

in the United States, 181, 183. 
as affected by moisture, 183. 
as affected by temperature, 183. 

rainfall, 199, 200, 203-207. 

rust, 185, 191. 

seed, 252. 

seeding and harvesting, 185, 188, 
189. 
to escape damage by hessian 
fly, 189. 

snow-cover, 202. 

snowfall, 202, 203. 

temperature, 199-207. 

winter-killing, 208, 209. 

zero of vital temperature, 68. 
Winter-kilHng of wheat, 208, 209. 
Winter oats, 175. 
Wood fires, 279, 280. 

Zero of effective temperature, 67, 

68. 
Zero of vital temperature, 67, 68. 

a new zero suggested, 67, 68. 

for most crops, 68. 
Zones, climatic, 63. 



I*rinted in the United States of America 



